(currently incomplete reading notes)

Is it dark down there Where the grass grows through the hair? Is it dark in the under-land of Null? Helen Adam, ‘Down There in the Dark’, 1952

The void migrates to the surface . . . Advances in Geophysics, 2016

The rift’s edges are smoothed to a shine by those who have gone this way before, passing through the old ash to enter the underland.

Beneath the ash tree, a labyrinth unfurls.

Above is solid rock, utter matter. The surface is scarcely thinkable.

The passage is taken; the maze builds. Side-rifts curl off. Direction is difficult to keep. Space is behaving strangely – and so too is time. Time moves differently here in the underland. It thickens, pools, flows, rushes, slows.

Deep in an extinct volcano a tunnel network has been bored above a crustal fault known as Ghost Dance. Access drifts incline through tilted strata to level out in a repository zone, organized into emplacement corridors. The intent is to inter high-level nuclear waste in these corridors: radioactive uranium pellets encased in iron, then encased in copper, then buried above the Ghost Dance fault to pulse out their half-lives for millions of years to come. The timescale of the hazard is such that those responsible for entombing this waste must now face the question of how to communicate its danger to the distant future. This is a risk that will outlast not only the life of its makers but perhaps also the species of its makers. How to mark this site? How to tell whatever beings will come to this desert place that what is kept in this rock sarcophagus is desperately harmful, is not of value, must never be disturbed?

The same three tasks recur across cultures and epochs: to shelter what is precious, to yield what is valuable, and to dispose of what is harmful. Shelter (memories, precious matter, messages, fragile lives). Yield (information, wealth, metaphors, minerals, visions). Dispose (waste, trauma, poison, secrets). Into the underland we have long placed that which we fear and wish to lose, and that which we love and wish to save.

We know so little of the worlds beneath our feet. Look up on a cloudless night and you might see the light from a star thousands of trillions of miles away, or pick out the craters left by asteroid strikes on the moon’s face. Look down and your sight stops at topsoil, tarmac, toe.

In China’s Chongqing province, a cave network explored in 2013 was found to possess its own weather system: ladders of stacked mist that build in a huge central hall, cold fog that drifts in giant cloud chambers far from the reach of the sun. A thousand feet underground in northern Italy, I abseiled into an immense rotunda of stone, cut by a buried river and filled with dunes of black sand. Traversing those dunes on foot was like trudging through a windless desert on a lightless planet.

Why go low? It is a counter-intuitive action, running against the grain of sense and the gradient of the spirit. Deliberately to place something in the underland is almost always a strategy to shield it from easy view. Actively to retrieve something from the underland almost always requires effortful work. The underland’s difficulty of access has long made it a means of symbolizing what cannot openly be said or seen: loss, grief, the mind’s obscured depths

An aversion to the underland is buried in language. In many of the metaphors we live by, height is celebrated but depth is despised. To be ‘uplifted’ is preferable to being ‘depressed’ or ‘pulled down’. ‘Catastrophe’ literally means a ‘downwards turn’, ‘cataclysm’ a ‘downwards violence’. A bias against depth also runs through mainstream conventions of observation and representation.

buried

Time is profoundly out of joint – and so is place. Things that should have stayed buried are rising up unbidden. When confronted by such surfacings it can be hard to look away, seized by the obscenity of the intrusion.

In the Arctic, ancient methane deposits are leaking through ‘windows’ in the earth opened by melting permafrost. Anthrax spores are being released from reindeer corpses buried in once-frozen soil, now exposed by erosion and warmth. In the forests of Eastern Siberia a crater is yawning in the softening ground, swallowing tens of thousands of trees and revealing 200,000-year-old strata: local Yakutian people refer to it as a ‘doorway to the underworld’. Retreating Alpine and Himalayan glaciers are yielding the bodies of those engulfed by their ice decades before. Across Britain, recent heatwaves have caused the imprints of ancient structures – Roman watchtowers, Neolithic enclosures – to shimmer into view as crop-marks visible from above: aridity as X-ray, the land’s submerged past rising up in parched visitation. Where the River Elbe flows through the Czech Republic, summer water levels have recently dropped so far that ‘hunger stones’ have been uncovered – carved boulders used for centuries to commemorate droughts and warn of their consequences.

One of the hunger stones bears the inscription ‘Wenn du mich siehst, dann weine’: ‘If you see me, weep.’ In north-west Greenland an American Cold War missile base, sealed under the ice cap fifty years ago and containing hundreds of thousands of gallons of chemical contaminants, has begun to move towards the light. ‘The problem,’ writes the archaeologist Þóra Pétursdóttir, ‘is not that things become buried deep in strata – but that they endure, outlive us, and come back at us with a force we didn’t realise they had . . . a dark force of “sleeping giants”’, roused from their deep time slumber.

‘Deep time’ is the chronology of the underland. Deep time is the dizzying expanses of Earth history that stretch away from the present moment. Deep time is measured in units that humble the human instant: epochs and aeons, instead of minutes and years. Deep time is kept by stone, ice, stalactites, seabed sediments and the drift of tectonic plates. Deep time opens into the future as well as the past. The Earth will fall dark when the sun exhausts its fuel in around 5 billion years. We stand with our toes, as well as our heels, on a brink.

There is dangerous comfort to be drawn from deep time. An ethical lotus-eating beckons. What does our behaviour matter, when Homo sapiens will have disappeared from the Earth in the blink of a geological eye? Viewed from the perspective of a desert or an ocean, human morality looks absurd – crushed to irrelevance. Assertions of value seem futile. A flat ontology entices: all life is equally insignificant in the face of eventual ruin. The extinction of a species or an ecosystem scarcely matters in the context of the planet’s cycles of erosion and repair

deep time as a radical perspective, provoking us to action not apathy. For to think in deep time can be a means not of escaping our troubled present, but rather of re-imagining it; countermanding its quick greeds and furies with older, slower stories of making and unmaking. At its best, a deep time awareness might help us see ourselves as part of a web of gift, inheritance and legacy stretching over millions of years past and millions to come, bringing us to consider what we are leaving behind for the epochs and beings that will follow us.

When viewed in deep time, things come alive that seemed inert. New responsibilities declare themselves. A conviviality of being leaps to mind and eye. The world becomes eerily various and vibrant again. Ice breathes. Rock has tides. Mountains ebb and flow. Stone pulses. We live on a restless Earth.

A variant to the Epic of Gilgamesh – written around 2100 BC in Sumeria – tells of such a descent, made by Gilgamesh’s servant Enki to the ‘netherworld’ on behalf of his master to retrieve a lost object. Enki sails through storms of hailstones that strike him like ‘hammers’, his boat trembles from the impact of waves that attack it like ‘butting turtles’ and ‘lions’, but still he reaches the netherworld. There, however, he is promptly imprisoned – only to be freed when the young warrior Utu opens a hole to the surface and carries Enki back out on a lofting breeze. Up in the sunlight Enki and Gilgamesh embrace, kiss, and talk for hours. Enki has not retrieved the lost object, but he has brought back precious news of vanished people. ‘Did you see my little stillborn children who never knew existence?’ asks Gilgamesh desperately. ‘I saw them,’ answers Enki.

Classical literature records numerous instances of what in Greek were known as the katabasis (a descent to the underland) and the nekyia (a questioning of ghosts, gods or the dead about the earthly future)

darkness might be a medium of vision, and that descent may be a movement towards revelation rather than deprivation.

Our common verb ‘to understand’ itself bears an old sense of passing beneath something in order fully to comprehend it. ‘To discover’ is ‘to reveal by excavation’, ‘to descend and bring to the light’, ‘to fetch up from depth’. These are ancient associations. The earliest-known works of cave art in Europe – taking the form of painted ladders, dots and hand stencils on the walls of Spanish caves – have been dated to around 65,000 years ago, some 20,000 years before Homo sapiens are believed to have first arrived in Europe from Africa.

I have for some time now been haunted by the Saami vision of the underland as a perfect inversion of the human realm, with the ground always the mirror-line, such that ‘the feet of the dead, who must walk upside down, touch those of the living, who stand upright’.

The first of the objects is a double-cast bronze casket the size of a swan’s egg, which sits heavy in the hand. It is a kist and what it contains is toxic. Its maker wrote his demons down on a sheet of paper: his hatreds, fears and losses, the pain he had inflicted on others and the pain others had inflicted on him – all that was worst in his mind. Then he burned the paper and sealed the ashes inside the casket. Then he double-cast the casket, giving it a second layer of bronze to increase the strength of the containment. That outer layer of bronze became pitted and encrusted in the process of its casting, such that it seemed to resemble either the surface of a planet or the weather above it. Then he drove four iron nails through the casket’s centre, cutting off their ends and filing them flush. It is an exceptionally powerful object, which possesses a ritual intensity of creation. It could have been fashioned at any point in the past 2,500 years, but it was made only recently. I was given the casket on the condition that I disposed of it in the deepest or most secure underland site that I reached – a place from which it could never return.

The second of the objects is an owl cut from a slice of whalebone. It is a talisman and what it connotes is magic. The minke whale from which the owl was taken had washed up dead on the shoreline of a Hebridean island. One of its rib bones was smoothed into cross-sections, each less than half an inch thick and six inches high. One of those cross-sections was then cut into the form of an owl with four bold strokes of a blade: two strokes for the eyes, and two for the wing lines. It is an exceptionally beautiful object, which possesses an Ice Age simplicity of making. It could have been fashioned at any point in the past 20,000 years, but it was made only recently. I was given the owl on the condition that I carried it with me at all times in the underland, to help me see in the dark.

We are often more tender to the dead than to the living, though it is the living who need our tenderness most.

the great descent stories of underworld mythology – Dante and Virgil, Persephone and Demeter, Eurydice, Orpheus and Aristaeus (the keeper of bees)

unearthed and unearthly

The first fact of limestone is its solubility in water. Rain absorbs carbon dioxide from the air, creating a mild carbonic acid – just sharp enough to etch and fret limestone, given time. This fretwork deepens into limestone’s surface perforations of gryke and clint, and also its hidden labyrinths of rift and chamber. Streams shape stone with their energy. Thermal waters rise from within the earth, biting rock into form. Limestone landscapes are rich with clandestine places. They have the unexpected volumes of a lung’s interior. Portals give access to their extensive underland: pots and sinkholes, swallets where streams vanish into their own beds.

Tim Robinson, knows the deceptions of limestone better than almost anyone. After living on and mapping limestone for more than forty years, he concludes: ‘I do not trust space an inch.’

‘It’s a petrifying stream,’ Sean says. ‘There’s so much calcium carbonate dissolved in it that any twigs or leaves snagged there soon pick up a white crust of stone.’

‘Look at this,’ Sean says, pointing upwards. Where the lowest bough of an old alder meets its trunk, one end of a curved metal blade protrudes. The rest of the object is lost below the bark. ‘It’s a scythe. Someone hooked it up on here many decades ago and forgot about it. So the tree absorbed the blade, growing around it while the handle rotted away.’

Everywhere I look there is evidence of burial and excavation. Badger setts, molehills, bee tunnels, the engulfed scythe, the hives, the entrances to mine adits. Even the house, set back into the dolomite slope, is part cave.

‘Then there are the burial sites – Bronze Age bowl barrows mostly, but Neolithic long barrows too, and of course, at Aveline’s, the Mesolithic chamber. Medieval and early modern graveyards, and then our own still-growing cemeteries. This has been a funerary landscape for over 10,000 years. It’s a terrain into which we have long entrusted things, as well as from which we have long extracted things.’

‘To be human means above all to bury,’ declares Robert Pogue Harrison in his study of burial practices, The Dominion of the Dead, boldly drawing on Vico’s suggestion that humanitas in Latin comes first and properly from humando, meaning ‘burying, burial’, itself from humus, meaning ‘earth’ or ‘soil’. We are, certainly, a burying species as well as a building species – and our predecessors were buriers too.

In burial, the human body becomes a component of the earth, returned as dust to dust – inhumed, restored to humility, rendered humble. Just as the living need places to inhabit, so it is often in the nature of our memory-making to wish to be able to address our dead at particular sites on the Earth’s surface. The burial chamber, the gravestone, the hillside on which ashes have been scattered, the cairn: these are places to which the living can return and where loss might be laid to rest. The grief of those who have been unable to locate the bodies of their loved ones can be especially corrosive – acid and unhealing.

Limestone, in particular, has long been a geology of burial – in part because it is so common globally, in part because its erosive tendencies create so many natural crypts into which bodies may be laid, and in part because limestone is itself, geologically speaking, a cemetery. Limestone is usually formed of the compressed bodies of marine organisms – crinoids and coccolithophores, ammonites, belemnites and foraminifera – that died in waters of ancient seas and then settled in their trillions on those seabeds. These creatures once built their skeletons and shells out of calcium carbonate, metabolizing the mineral content of the water in which they lived to create intricate architectures. In this way limestone can be seen as merely one phase in a dynamic earth cycle, whereby mineral becomes animal becomes rock; rock that will in time – in deep time – eventually supply the calcium carbonate out of which new organisms will build their bodies, thereby re-nourishing the same cycle into being again.

Around 27,000 years ago, on a limestone hillside overlooking what is now the Austrian Danube, two babies, dead at birth, were placed side by side in a freshly dug round hole. Their remains were wrapped in animal hide, and the space around them was packed with red ochre, into which were mixed yellow beads of ivory. A shelter was then constructed to protect them from the crushing embrace of the earth: a scapula from a woolly mammoth, propped up as a bone shroud on pieces of tusk.

Twelve thousand years ago in a limestone cave above the Hilazon River in what is now northern Israel, a grave was prepared for a woman in her forties. An oval hole was dug in the cave floor, and its sides were walled with limestone slabs. Her body was placed in the grave, curled against the northern side of the oval. Two stone martens, their brown and cream fur sleek in the low light, were draped over her: one across her upper body, one across her lower. The foreleg of a wild boar was laid on her shoulder. A human foot was placed between her feet. The blackened shells of eighty-six tortoises were scattered over her. The tail of an aurochs was put near the base of her spine. The wing of a golden eagle was opened over her. She had become a wondrous hybrid – a being of many beings. At last, a single large plate of limestone was pulled over the hole, closing this compound creature inside her chamber.

We tend to imagine stone as inert matter, obdurate in its fixity. But here in the rift it feels instead like a liquid briefly paused in its flow. Seen in deep time, stone folds as strata, gouts as lava, floats as plates, shifts as shingle. Over aeons, rock absorbs, transforms, levitates from seabed to summit. Down here, too, the boundaries between life and not-life are less clear.

The cascade is a baroque structure. Flowstone is the name given to the calcite deposits that precipitate out of minerally saturated water as it runs over the slopes of limestone caves. You might imagine flowstone as a kind of white candle wax, gradually hardening as it runs, though it is built up over spans of time rather than by brief incandescence. Because of the gradual nature of its formation, flowstone sets into elaborate ruches and folds – elephant-skin gathers of texture, wrinkled stockings. Flowstone is very beautiful to look at and very hard to grip.

The most notorious story in British caving history involves a twenty-year-old Oxford philosophy student called Neil Moss. It is still, in my experience, a story that some people in the Peak District do not like to discuss, nearly sixty years on

Cement powder from the local works was carried into the cave, mixed with water from the thigh-deep lake, and then poured down the pot, entombing Moss in perpetuity. This section of Peak Cavern is now known as Moss Chamber.

Ahead of us is the shoulder-wide entrance to the ruckle. ‘This is a space granted by collapse,’ says Sean quietly, admiringly. A ruckle is a group of boulders that have caved against one another, blocking a section of passage, but through the gaps of which a path might just be traced.

stubborn, unshrinkable human bodies.

In that vanishing point, neither of us speaks. Language is crushed

Meadowsweet, knapweed, scabious. Everything is shiveringly strange. Flies on the grass blades are exotic as tigers – eyes of a thousand ruby hexagons, wings of the finest filigree.

We are often more tender to the dead than to the living, though it is the living who need our tenderness most . . .

More than half a mile under the earth, in a laboratory set into a band of translucent silver rock salt left behind by the evaporation of an epicontinental northern sea some 250 million years earlier, a young physicist is trying to look into a void. He sits watching a computer screen, close to a large silver cube. The cube’s name is DRIFT and it is a breath-catcher. The young physicist is trying to catch the faint breath of a particle wind sent blowing across space from a constellation called Cygnus, the Swan, many light years distant from Earth.

How, though, to hunt for darkness in darkness? How to seek a substance that has mass and therefore exerts gravity, but that does not emit light, reflect it or block it? Since Zwicky, the evidence for the existence of dark matter has been gathered largely by inference: the detection not of the matter itself, but of its presumed influence on luminous entities, observable objects. To perceive matter that casts no shadow, you must search not for its presence but for its consequence.

Noise is the trundle of everyday particles through the air, the din of the ordinary atomic world going about its business. Radioactivity is deafening noise. Cosmic-ray muons are noise. If you wish to listen for sounds so faint they may not exist at all, you can’t have someone playing the drums in your ear. To hear the breath of the birth of the universe, you must come below ground to what are, experimentally speaking, among the quietest places in the universe.

‘annihilation products’,

DRIFT: directional recoil identification from tracks.

This network of tunnels and roadways is collectively known as ‘drift’. There are more than 600 miles of existing drift burrowed into the soft bands of halite (salt) and sylvite (potash) that stretch below sea and land, out to the mining faces where – every hour of every year – men and machines claw tons of potash from the seams, duct the potash onto hoppers and start the journey of this buried residue of a Permian sea up to the world’s crop fields, where it will be spread as a fertilizer in both of the Earth’s annual two springs, returning vital potassium to the growing cycle.

Salt has very low gamma radiation. Salt is a good insulator. Salt is radio-pure. Salt is an excellent substance in which to encase yourself if you want to study weakly interacting massive particles. But salt is also highly plastic. Salt flows over time. It creeps around. It sags. If you cut a chamber out of a seam of halite with 3,000 feet of bedrock above it, that chamber will slowly distort. The ceiling will dip, the sides will bulge. Gravity wants that space back. So the scientists working in the Boulby laboratory know they are operating in a temporary zone, with limited years of safe life. Deep time must be studied fast.

From the outside, the magnificently named Time Projection Chamber is disappointing to look at. Black bin liners are taped scruffily around a large metal-clad box. ‘I see that bin bags make up the vital outer layer of your crystal ball,’ I say. ‘You mock,’ replies Christopher, ‘but duct tape and bin bags have proved crucial to more scientific breakthroughs than you’d imagine.’

I will learn over the years ahead that many such Chinese-box structures, with their multiple containment protocols, characterize storage procedures in the underland, from the falcon-headed Canopic stone jars of ancient Egyptian burial practice – into which were placed the vital organs of the dead, and which were themselves encased in a painted wooden chest, itself encased in a tomb, itself encased in a pyramid – to the concentric sheathing of spent uranium pellets from nuclear reactors; the pellets placed within rods of zirconium, the rods encased in a copper cylinder, the copper cylinder encased in an iron cylinder, the iron cylinder encased in bentonite clay rings, and the rings encased in the bedrock of a deep geological storage facility, sunk thousands of feet into gneiss, or granite, or salt.

‘Everything causes a scintillation.’ He pauses. ‘Why are you searching for dark matter?’ I ask. ‘To further our knowledge,’ Christopher replies without hesitation, ‘and to give life meaning. If we’re not exploring, we’re not doing anything. We’re just waiting.’ He pauses again. I wait.

‘My sense,’ I say to Christopher, ‘is that the search for dark matter has produced an elaborate, delicate edifice of presuppositions, and a network of worship sites, also known as laboratories, all dedicated to the search for an invisible universal entity which refuses to reveal itself. It seems to resemble what we call religion rather more than what we call science.’ ‘I grew up as a very serious Christian,’ Christopher says. ‘Then I lost my faith almost entirely when I found physics. Now that faith has returned, but in a much-changed form. It’s true that we dark-matter researchers have less proof than other scientists in terms of what we seek to discover and what we believe we know. As to God? Well, if there were a divinity then it would be utterly separate from both scientific enquiry and human longing.’

The strains of the work are intense, the lifespan of the machines short. ‘When one of them reaches the end of its useful days,’ says Neil, ‘it’s not cost-effective to bring it back up. It’d take the place of ore in the upshaft, and that’s too expensive. So instead the machine gets driven into a worked-out tunnel of rock salt, and abandoned there. The halite will flow around it as the tunnel naturally closes up.’ It is an astonishing image: the translucent halite melting around this cybernetic dragon – the fossilization of this machine-relic in its burial shroud of salt.

In the halite strata that underlie the New Mexico desert, an underground facility known as the Waste Isolation Pilot Plant has been excavated, designed for the long-term disposal of transuranic radioactive waste arising from the research and production of nuclear weapons. More than 2,000 feet below the desert surface, a burial site has been created for thousands of silver steel drums packed with nuclear waste.

I am briefly filled with a longing to step into a side tunnel myself, lie down and let the halite slowly seal me in for five years or 10,000 – to wait out the Anthropocene in that translucent cocoon.

In 1999, at a conference in Mexico City on the Holocene – the epoch of Earth history that we at present officially inhabit, beginning around 11,700 years ago – the Nobel Prize-winning atmospheric chemist Paul Crutzen was struck by the inaccuracy of the Holocene designation. ‘I suddenly thought this was wrong,’ he later recalled. ‘The world has changed too much. So I said, “No, we are in the Anthropocene.” I just made the word up on the spur of the moment. But it seems to have stuck.’

As the Pleistocene was defined by the action of ice, and the Holocene by a period of relative climatic stability allowing the flourishing of life, so the Anthropocene is seen to be defined by the action of anthropos: human beings, shaping the Earth at a global scale.

Among the relics of the Anthropocene, therefore, will be the fallout of our atomic age, the crushed foundations of our cities, the spines of millions of intensively farmed ungulates, and the faint outlines of some of the billions of plastic bottles we produce each year – the strata that contain them precisely dateable with reference to the product-design archives of multinationals. Philip Larkin famously proposed that what will survive of us is love. Wrong. What will survive of us is plastic, swine bones and lead-207, the stable isotope at the end of the uranium-235 decay chain.

The Anthropocene asks of us the question memorably posed by the immunologist Jonas Salk: ‘Are we being good ancestors?’

Time feels differently reckoned after the mine: further deepened, further folded. My sense of nature feels differently reckoned too: further disturbed, further entangled. Somewhere to my east, men are at work a mile below the moors, half a mile under the sea, cutting tunnels through the salt-ghost of an ocean to harvest its energy for crops as yet ungrown. A Time Projection Chamber is waiting for signals from Cygnus, the Swan, that might tell something of the birth of the universe, 13.8 billion years earlier. A labyrinth of drift is slowly closing up, lizard-machines and Ford Transits are being sealed into their tombs of salt – and through it all is passing a particle wind of WIMPs and neutrinos, to which this world is as mere mist and silk.

Occasionally – once or twice in a lifetime if you are lucky – you encounter an idea so powerful in its implications that it unsettles the ground you walk on.

Simard’s enquiries confirmed that beneath her forest floor there did indeed exist what she called an ‘underground social network’, a ‘bustling community of mycorrhizal fungal species’ that linked sapling to sapling. She also discovered that the hyphae made connections between species: joining not only paper birch to paper birch and Douglas fir to Douglas fir, but also fir to birch and far beyond – forming a non-hierarchical network between numerous kinds of plants.

Suzanne Simard

The isotope tracking also demonstrated the unexpected intricacy of the interrelations. In a research plot thirty metres square, every single tree was connected to the fungal system, and some trees – the oldest – were connected to as many as forty-seven others. The results also solved the puzzle of the fir–birch mutualism: the Douglas firs were receiving more photosynthetic carbon from paper birches than they were transmitting. When paper birches were weeded out, the nutrient intake of the fir saplings was thus – counter-intuitively – reduced rather than increased, and so the firs weakened and died.

Seen in the light of Simard’s research, the whole vision of a forest ecology shimmered and shifted – from a fierce free market to something more like a community with a socialist system of resource redistribution.

Simard’s first major paper on the subject was published in Nature in 1997, and it was from there that the subterranean network of tree–fungus mutualism gained its durable nickname of ‘the wood wide web’.

New technologies of detection and mapping have illuminated fresh details of this ‘social network’ of trees and plants. ‘The wood wide web has been mapped, traced, monitored and coaxed,’ as Simard puts it, ‘to reveal the beautiful structures and finely adapted languages of the forest network.’

Merlin Sheldrake.

‘I’ve heard this called “pleaching”,’ I say to Merlin, patting the fused branches. ‘The artist David Nash planted a circle of ash trees in a clearing in North Wales, then bent and wove the trees so that they grew not just next to one another but into one another, a dancing “Ash Dome”, made of a meld of boughs and limbs.’ ‘Actually,’ says Merlin, ‘plant scientists have a technical term for this. We call it “snogging”, or to give it its full name, “tree snogging”.’ He smiles. ‘Well, not quite. The technical term is actually “inosculation”, from the Latin osculare, meaning “to kiss”. Inosculation means “to en-kiss”. It can happen across trees and between species too.’

‘My childhood superheroes weren’t Marvel characters,’ Merlin once said to me, ‘they were lichens and fungi. Fungi and lichen annihilate our categories of gender. They reshape our ideas of community and cooperation. They screw up our hereditary model of evolutionary descent. They utterly liquidate our notions of time. Lichens can crumble rocks into dust with terrifying acids. Fungi can exude massively powerful enzymes outside their bodies that dissolve soil. They’re the biggest organisms in the world and among the oldest. They’re world-makers and world-breakers. What’s more superhero than that?’

Epping extends to the north-east of London, and it is very far from a wildwood. It was first designated as a royal hunting forest in the twelfth century by Henry II, with penalties for poaching that included imprisonment and mutilation. Presently it is managed by the City of London Corporation, and has more than fifty bye-laws governing behaviour within its bounds – though the punishments are now fiscal rather than corporal. It is fully contained within the M25, the orbital motorway that encircles outer London. Minor roads traverse it, and it is never more than two and a half miles wide. Despite its small extent, Epping is easy to get lost in – a forest of forking paths to which, for a thousand years, the people of London and its surrounds have gone for shelter, sex, escape and a relic greenwood magic.

In the language of forestry and forest ecology, the ‘understorey’ is the name given to the life that exists between the forest floor and the tree canopy: the fungi, mosses, lichens, bushes and saplings that thrive and compete in this mid-zone. Metaphorically, though, the ‘understorey’ is also the sum of the entangled, ever-growing narratives, histories, ideas and words that interweave to give a wood or forest its diverse life in culture.

E. I. Newman’s classic 1988 paper, ‘Mycorrhizal Links between Plants: Their Functioning and Ecological Significance’.

mycelial network

Working with Rackham, Merlin found himself most intellectually attracted to places where orthodox evolutionary theory felt thinnest – and for him the thinnest places were where mutualisms were at work. Mutualism is a subset of symbiosis in which there exists between organisms a prolonged relationship that is interdependent and reciprocally beneficial.

‘Of course,’ I reply. ‘The ancient glowing-bobtail-squid-and-bacteria mutualism.’ ‘The ultimate mutualism, though,’ says Merlin, ‘is between plants and mycorrhizal fungi.’

A plant under attack from aphids can indicate to a nearby plant via the network that it should up-regulate its defensive response before the aphids reach it. It has been known for some time that plants communicate above ground in comparable ways, by means of diffusible hormones. But such airborne warnings are imprecise in their destinations. When the compounds travel by fungal networks, both the source and recipient can be specified. Our growing comprehension of the forest network asks profound questions: about where species begin and end, about whether a forest might best be imagined as a superorganism, and about what ‘trading’, ‘sharing’ or even ‘friendship’ might mean between plants and, indeed, between humans.

Pollarding – the pruning of the upper branches of a tree to promote dense growth – keeps trees alive for longer, indeed can enter them into an almost indefinite fairy-tale time of longevity.

beautiful phenomenon known as ‘crown shyness’, whereby individual forest trees respect each other’s space, leaving slender running gaps between the end of one tree’s outermost leaves and the start of another’s.

‘This is our problem when it comes to studying the fungal network,’ he says. ‘Soil is fantastically impenetrable to experiments, and the fungal hyphae are on the whole too thin to see with the naked eye. That’s the main reason it’s taken us so long to work out the wood wide web’s existence, and to discern what it’s doing.’

Rivers of sap flow in the trees around us. If we were right now to lay a stethoscope to the bark of a birch or beech, we would hear the sap bubbling and crackling as it moves through the trunk. ‘You can put rhizotrons into the ground to look at root growth,’ Merlin says, ‘but those don’t really give you the fungi because they’re too fine. You can do below-ground laser scanning but, again, that’s too crude for the fungal networks.’

What’s the haunting phrase I’ve heard used to describe the realm of fungi? The kingdom of the grey. It speaks of fungi’s utter otherness – the challenges they issue to our usual models of time, space and species. ‘You look at the network,’ says Merlin, ‘and then it starts to look back at you.’

All taxonomies crumble, but fungi leave many of our fundamental categories in ruin. Fungi thwart our usual senses of what is whole and singular, of what defines an organism, and of what descent or inheritance means. They do strange things to time, because it is not easy to say where a fungus ends or begins, when it is born or when it dies. To fungi, our world of light and air is their underland, into which they tentatively ascend here and there, now and then.

Fungi were among the first organisms to return to the blast zone around the impact point in Hiroshima, the point from which the mushroom cloud had risen. After Hiroshima, too, images of the mushroom cloud began to appear ubiquitously in media and culture – the fruiting bodies of a new global anxiety. Scientists working in Chernobyl after the disaster there were surprised to discover fine threads of melanized fungi lacing the distressed concrete of the reactor itself, where radiation levels were over 500 times higher than in the normal environment. They were even more surprised to work out that the fungi were actively thriving due to the high levels of ionizing radiation: that they benefited from this usually lethal gale, increasing their biomass by processing it in some way.

Ecologists in the US seeking to understand how American trees will respond to the stress of climate change have begun to focus on the presence of soil fungi as a key indicator of future forest resilience. Recent studies suggest that well-developed fungal networks will enable forests to adapt faster at larger scales to the changing conditions of the Anthropocene.

‘Learning to see mosses is more like listening than looking,’ writes the ethnobotanist Robin Wall Kimmerer; ‘mosses . . . issue an invitation to dwell for a time right at the limits of ordinary perception.’ Learning to see fungi seems even harder – requiring senses and technologies that we have yet to develop. Even to try and think with or as fungi is valuable, though, drawing us as it does towards lifeways that are instructively beyond our ken.

History no longer feels figurable as a forwards-flighting arrow or a self-intersecting spiral; better, perhaps, seen as a network branching and conjoining in many directions. Nature, too, seems increasingly better understood in fungal terms: not as a single gleaming snow-peak or tumbling river in which we might find redemption, nor as a diorama that we deplore or adore from a distance – but rather as an assemblage of entanglements of which we are messily part.

The fungal forest that science had revealed to Merlin and that Merlin was revealing to me – a forest of arborescent connections and profuse intercommunication – seemed merely to provide a materialist evidence-base for what the cultures of forest-dwelling peoples have known for thousands of years. Again and again within such societies, the jungle or woodland is figured as aware, conjoined and conversational.

I recall Kimmerer, Hardy and Nelson, and feel a sudden, angry impatience with modern science for presenting as revelation what indigenous societies take to be self-evident. I remember Ursula Le Guin’s angrily political novel, set on a forest planet in which woodland beings known as the Athsheans are able to transmit messages remotely between one another, signalling through the medium of trees. On Athshe – until the arrival of colonists committed to the planet’s exploitation – the realm of mind is integrated into the community of the trees, and ‘the word for world is forest’.

So I use my phone to summon the satellite network, and pull up a hybrid map of the forest. Sixty-three distinct chemical elements including rare earth metals and minerals mined mostly in China interact within the casing of my device. A blue lanthium dot pulses our location. I pinch and splay the screen to get the right scale. The map shows that the forest flares green to the south-west, so that is where we head – crossing a busy road and then pushing deeper into the trees until we can hardly hear car noise.

There was also ‘the Lightning Guy’, who studied the effects of lightning strikes on below-ground ecologies, and tried to induce site-specific strikes by firing crossbow bolts trailing copper wire at storm clouds.

Some of the science undertaken on the island was methodologically high risk.

‘mycoheterotrophs’ – ‘mycohets’ for short. Mycohets are plants that lack chlorophyll and thus are unable to photosynthesize. As such they are entirely reliant on the fungal network for their provision of carbon. Some are white, some tinged lilac or violet.

Voyria, a group of gentians known as ‘ghost plants’, the flowers of which studded the jungle floor on Barro Colorado Island like pale purple stars.

Science is full of this stuff: full of happenstance and stumbles and getting knackered and crazy in the field or the lab. It’s so weird to me how science always presents its knowledge as clean.’

‘I have this plan,’ Merlin says, ‘that for each formal scientific paper I ever publish I will also write its dark twin, its underground mirror-piece – the true story of how the data for that cool, tidy hypothesis-evidence-proof paper actually got acquired. I want to write about the happenstance and the shaved bumblebees and the pissing monkeys and the drunken conversations and the fuck-ups that actually bring science into being. This is the frothy, mad network that underlies and interconnects all scientific knowledge – but about which we so rarely say anything.’

In my field, discourse choice forcefully shapes research directions. “Sanction and reward”, for instance, is a central technical concept in mycorrhizal studies, not just an ornament of speech. The metaphor drives the scholarship. I read research papers with titles like “Unequal Goods Shared under Common Terms of Trade”.’ ‘That sounds as if it was commissioned by the Ayn Rand Think Tank,’ I say. ‘Indeed. Awful. Politically, I’m obviously inclined to dislike the language of biological free-marketry far more than the socialist version,’ says Merlin. ‘Why should we expect fungi and plants to behave as humans started to behave economically in the eighteenth century, with the emergence of the limited liability corporation? I find it so bizarre. It’s one reason I love the Voyria. They demand immediately that you go beyond cost-benefit analysis when thinking about plant life. ‘But I’m also sceptical of the socialist dream of fungi as sharing and caring, a rose-tinted vision that sees trees as nurses, every tree a carer to every other, with “mother trees” recognizing and talking with their kin, and “injured trees” selflessly passing on their legacies to neighbours before they die.

die. ‘I’m tired of both of these stories,’ Merlin says as we leave the lake. ‘The forest is always more complicated than we can ever dream of. Trees make meaning as well as oxygen. To me, walking through a wood is like taking a tiny part in a mystery play run across multiple timescales.’

‘Maybe, then, what we need to understand the forest’s underland,’ I say, ‘is a new language altogether – one that doesn’t automatically convert it to our own use values. Our present grammar militates against animacy; our metaphors by habit and reflex subordinate and anthropomorphize the more-than-human world. Perhaps we need an entirely new language system to talk about fungi . . . We need to speak in spores.’ ‘Yes,’ says Merlin with an urgency that surprises me, smacking his fist into the palm of his hand. ‘That’s exactly what we need to be doing – and that’s your job,’ he says. ‘That’s the job of writers and artists and poets and all the rest of you.’

Potawatomi, a Native American language of the Great Plains region, includes the word puhpowee, which might be translated as ‘the force which causes mushrooms to push up from the earth overnight’. In ‘all its technical vocabulary’, Robin Wall Kimmerer notes, ‘Western science has no such term, no words to hold this mystery.’

Kimmerer herself is a member of the Citizen Potawatomi Nation. A speaker of what she calls ‘fluent botany’, she is careful to distinguish this from what she refers to as ‘the language of plants’ – that is to say, the language that plants speak, as opposed to the language that is used to speak of plants.

a ‘grammar of animacy’.

The real underland of language is not the roots of single words, but rather the soil of grammar and syntax, where habits of speech and therefore also habits of thought settle and interact over long periods of time. Grammar and syntax exert powerful influence on the proceedings of language and its users. They shape the ways we relate to each other and to the living world. Words are world-makers – and language is one of the great geological forces of the Anthropocene.

Projects have recently been started around the world to gain even the most basic of vocabularies for the experiences of life and death in the Anthropocene. These stuttering attempts to speak what it is we are doing have generated ugly new terms for an ugly epoch: ‘geotraumatics’, ‘planetary dysphoria’, ‘apex-guilt’. Such words feel like futile forms of nominalism, a hopelessly hyperactive pointing and naming. They stick in the throat in two ways: they are difficult to utter and hard to swallow.

‘species loneliness’,

‘Home-made cider,’ he says. The brown glass of the bottle carries a single white label, on which is written the word ‘Gravity’. ‘I pressed this from some windfall apples that had fallen from Newton’s apple tree in Cambridge. It’s quite hard to get to, that tree. It’s in Trinity College. Security is reasonably tight. The scrumping had to be done under cover of night. I wish I could have brought us a bottle of the first ever batch we made. That was from apples scrumped from Darwin’s orchard at Down House. You can probably guess the label name for that batch.’

I remember something Louis de Bernières has written about a relationship that endured into old age: ‘we had roots that grew towards each other underground, and when all the pretty blossom had fallen from our branches we found that we were one tree and not two.’ As someone lucky to live in a long love, I recognize that gradual growing-towards and subterranean intertwining; the things that do not need to be said between us, the unspoken communication which can sometimes tilt troublingly towards silence, and the sharing of both happiness and pain. I think of good love as something that roots, not rots, over time, and of the hyphae that are weaving through the ground below me, reaching out through the soil in search of mergings. Theirs, too, seems to me then a version of love’s work.

Something odd is happening in this quarry now, though. Men from a ministry have come, and they have paid for five of the caverns cut inside the mountain to be converted into bunkered treasure rooms. Small brick houses have been constructed inside the caverns, their interiors air-conditioned and temperature-controlled. And up the old quarry road have laboured lorries containing hundreds of large, thin packages. The packages are paintings: Claude’s Landscape with David at the Cave of Adullam, Piombo’s Raising of Lazarus, Van Dyck’s eleven-foot-high version of Charles I mounted on a horse, work by Gainsborough, Hogarth, Constable, Turner and Monet. All of these paintings have been taken under armed guard from the National Gallery in London and transported to this cored-out Welsh mountain, to be placed in these brick chambers under 300 solid feet of 400-million-year-old slate – safe, surely, here of all places, from the bombs of the Luftwaffe.

(Nidder – a variant of ‘nether’; to ‘nidder’ or ‘nether’ is to ‘keep down’, to ‘press under’)

Inside a tent made from shrapnel-torn sheets of white plastic a shaft has been dug into sandy soil. It drops fifty feet vertically, at which point a tunnel just high enough for a man to stand in extends laterally for 900 feet, to where a similar shaft rises to the surface, its mouth also concealed by a tent. The two shafts are separated by a national border. The illegal tunnel is a means of evading a punitive blockade on the movement of goods across this boundary. There are hundreds of similar tunnels, riddling the underland below the frontier, and along them are smuggled supplies of food, clothes, hardware, people, livestock and weaponry. When war flares here, as it does often, air-strikes target the tunnels with fighter planes dropping one-ton bombs in an attempt to destroy what is buried.

A door is set into a wedge of concrete which angles back into a mountainside, high on an Arctic island. The roof of the portal radiates an otherworldly green – an installation of prisms is reflecting the aurora borealis that are shimmering in the polar night sky. Prophecies of the world’s end in fire have receded; now the eschatology is one of ongoing breakdown rather than apocalypse. The end times are here, present, all around now, no longer deferrable. The heavy doorway opens into a tube of corrugated metal sloping deep into the mountain, far above sea level. This is a doomsday vault, made to survive for as close to eternity as can be reached on Earth. The frosted vaults of this eschaton, quarried from the limestone of the island, hold not people – but seeds.

The seeds bide their time.

The name that will be given to this discovered city is Derinkuyu, meaning ‘Deep Well’. Its excavation is thought to have begun in the fourth century BC, and for more than a thousand years it has provided a place in which persecuted minorities might hide until trouble has passed. From a far chamber of the city, a five-mile-long passage connects this city to another such sunken city, even larger in extent. The man has stumbled into an invisible city – no, a network of invisible cities

The map runs to sixteen laminated foolscap pages, or about ten square feet in area when I tile the pages together. I have been given it on the condition that I do not pass it on. It is not like any map I have ever seen and I have seen some strange maps in my time.

The invisible city exists across multiple levels of depth, each connected to the other by staircases and wells. These sites of juncture between the levels are marked on the map with orange rings (for wells with rung ladders), blue rings (for wells with sheer sides) and segmented dark blue circles (for staircases). Deeper-down layers and systems are shaded in darker inks. I learn to let my eyes go lazy, so that one level swims above another and I can perceive the different strata of the under-city.

The map’s place names traverse a range of cultural registers, from the classical to the surreal to the military-industrial. The Room of Cubes. The Passage of the Claustrophile. The Boutique of Psychosis. Crossroads of the Dead. The Clinic of the Aliens. The Chamber of Phantoms. The Medusa. The Glazery. The Maze of Montsouris. The Bermudas. The Shelter of the Little Leaves. The Monastery of the Bears. Bunker under the Mountain. The Cabinet of Mineralogy. The School of Mines. The Chamber of Oysters. Ossa Arida. Stairways of the Ossuary. Room Z.

On the cover page of the map, a link is given to an ‘Encyclopedia of the Underground World’. Authorship is attributed only to a collective called ‘Nexus’ – ‘the connection or connections between the parts of a system or a group of entities’.

Between 1927 and 1940 – the year in which he sought to flee France into the safety of Spain, only to commit suicide in a hotel room in the Pyrenean border village of Portbou – Walter Benjamin compiled one of the most extraordinary city-texts ever written. The Passagen-Werk, as it is known in German – The Arcades Project in English – is a fragmentary, unfinished meditation on the topography, history and humanity of Paris, running to more than a thousand pages at the time of Benjamin’s death. Its form may be compared to a constellation or galaxy, the individual stars of which he drew together over more than a decade, collecting notes, quotations, aphorisms, stories and reflections in dozens of dossiers that he called Konvolute – ‘convolutes’ in English, meaning ‘coils’, ‘twists’, ‘enfoldments’ – each of which was identified by a letter.

Throughout The Arcades Project, scenes from Paris’s past flicker back into being. ‘It is more arduous to honour the memory of anonymous beings than that of the renowned,’ Benjamin remarked in the preliminary notes for his essay ‘Theses on the Philosophy of History’; the ‘construction of history is consecrated to the memory of the nameless’

Benjamin was fascinated by the existence of such portal points in the city. He wrote of the need to ‘make some sign to the world one is leaving’ when a threshold to the underworld was traversed, of the ‘hatchway[s] leading from the surface to the depths’, and of the penates that ‘guard the threshold’ and ‘protect and mark the transitions’.

The most subterranean of the convolutes in The Arcades Project is Convolute C, which contains Benjamin’s work on both the catacombs and the quarry voids of Paris. It is in Convolute C that Benjamin proposes his vision of Paris’s invisible city, filled with ‘lightning-scored, whistle-resounding darkness’.

cataflics

All cities are additions to a landscape that require subtraction from elsewhere.

subsidence sinkholes known as fontis that were reputed to be of diabolic origin.

Louis XVI responded shortly after his accession by creating an inspection unit for the ‘Quarries Below Paris and Surrounding Plains’, headed by a general inspector called Charles-Axel Guillaumot, and tasked with regulating the quarries for the purposes of public safety. It was Guillaumot who initiated the first mapping of the void network, with a view to consolidating existing spaces and regulating further quarrying activities

The result over centuries was a growing glut of the dead. Saints-Innocents became the resting place for millions of bodies. In an attempt to maximize the available space, ancient remains were exhumed from the earth and their bones were sorted and packed into galleries known as charniers, built within the curtilage of the cemetery. The main area of the cemetery was also built up with soil carted in from elsewhere, forming a dome of earth up to six feet above the previous ground level. But this, too, soon had a surfeit of rotting bodies.

In 1786 the process began of evacuating the city’s cemeteries, crypts and tombs of their dead, and transferring the remains of more than 6 million corpses to the quarry region known as the Tombe-Issoire, soon to become Les Catacombes, on what was then the Montrouge Plain. A grim, ritualized production line was established for this task, involving diggers, cleaners, stackers, drivers, porters and overseers. Every night for years, horse-drawn funerary wagons containing the bones of the disinterred dead, covered with heavy black cloths, preceded by torchbearers and followed by priests who chanted the Mass of the Dead, clopped through the streets from the cemeteries to the Tombe-Issoire, where they disposed of their contents. Down in the tunnels, workers sorted the remains of the dead, filing them by bones into space-efficient ricks and stacks. Minor forms of folk art emerged in the disposition of these bones: serried ranks of femurs, their gleaming lines separated by rows of skulls, all turned eye sockets outwards.

Felix Nadar would pioneer low-light photography techniques down in these ossuaries.

Adaptable quarrymen made a career move into mushroom farming, and a subterranean Horticultural Society of Paris was founded, its first president being a former general inspector of the mines. By 1940 there were some 2,000 mushroom farmers working underneath Paris.

cataphiles

cataflics

catacops

A commune culture emerged, with its own honour codes. The rules were few, and clear. Respect the past of the catacombs. Take out what you take in. Resources are to be shared, even with strangers. No selling and no buying: barter-exchange or gift are the only acceptable modes of transaction. Help is to be given wherever necessary. Create with care – and do not destroy. Some of the cataphiles went down to party. Others, though, became fascinated by the layered histories of the space.

Once, a pop-up cinema was established in one of the chambers, and themed films were shown over several weeks – Vertov’s Man with a Movie Camera, Lynch’s Eraserhead – until it was shut down by the cataflics. New rooms continue to be dug by cataphiles and new nameplates added to tunnels. Work groups are established to add fresh layers to the catacomb palimpsest: large graffiti murals, new carvings, a sword buried in a stone, or mosaic works involving thousands of tiles.

On a clean-cut wall of stone close to the entrance to our room are lines of cursive handwriting in black ink or paint. They record the names of quarrymen, the dates of completion of rooms and tunnels, and numbers of metres of stone cut on different days. Years are written by the different lines, starting in the late 1700s and running to the early 1800s. There is a pride to the making of this archive – and care has been taken to preserve it, too.

the bone owl and the bronze casket-egg

Calvino

the narrator describes the impossible city of Eusapia, in which inhabitants of the living city have accompanied ‘an identical copy of their city, underground’, a ‘Eusapia of the dead’ which can be accessed only by a confraternity of hooded brothers – though over time the symmetry between upper and lower cities becomes so acute that ‘in the twin cities there is no longer any way of knowing who is alive and who is dead.’

in one area of the Parisian catacombs, a quarryman and former soldier named Beauséjour Décure dedicated his spare time to carving intricate scale models of the Minorcan town of Port-Mahon into the living limestone.

Below the San Lorenzo Maggiore cathedral in Naples, writes geographer Wayne Chambliss, ‘there is a layer of urban stratigraphy containing an earlier, wholly intact iteration of the city. Streets, apartment complexes, storefronts, all filled in centuries ago and built over, have been unearthed below ground.’

Pierre Bélanger estimates that the ‘infrastructure that supports urban life’ now spans from ‘10,000 metres below the sea to 35,000 km above the surface of the earth’.

The catacomb labyrinth had become what we would now call a ‘dark site’ – an extra-jurisdictional space where special rendition of political prisoners could occur, out of public sight and mind.

I am in a vertical shaft and above me is a suspended wall of clay and earth, perhaps ten feet high, into which hundreds of human bones are embedded: skulls, ribs and limbs. In the belly of the well below are hundreds more fallen bones. It is a point where a burial ground has begun to disgorge its contents down through a breach in the tunnel network. The rough limestone from which the shaft has been hewn is also visibly thick with bodies – whelks and spiral shells that are fossilized uncrushed in the stone’s sediment

she smiles. ‘Or perhaps the ghost of Philibert Aspairt, lost down here in 1793 and not discovered until eleven years later. Dead, obviously. Arguably the world’s first urban explorer, and probably the worst.’

Urban exploration might best be defined as adventurous trespass in the built environment.

Urban explorers shun the Sturm und Drang of mountains. Their thrills are niche, their epiphanies mucky. Rumours circulate about entry points which might give access to unseen spaces. Secrets are jealously guarded, closely shared

Ruinistas dig ‘derp’ (explorer’s slang for ‘derelict and ruined places’). Detroit was the world mecca for derp, until it became a city-sized version of Don DeLillo’s ‘most photographed barn in America’, cloaked in a haze of voyeuristic ruin-porn imagery (HD stills of dusty ballrooms and atria, with artfully scattered detritus in the foreground, images that erase a hundred aspects of that city’s hope and despair).

At the avant-garde of urban exploration are the infiltrators, the ‘real’ explorers, who tend to be more stimulated by systems and networks than by single sites, and who cherish the challenge involved in accessing super-secure locations. Like extreme climbers, infiltrators experience what Al Alvarez called ‘feeding the rat’, in his classic essay on climbing and fear. They are obsessives: they develop tunnel vision. They run tracks in the brief gaps between trains, they take dinghies down storm drains, they lift-surf – and occasionally they die.

At its more political fringes, urban exploration mandates itself as a radical act of disobedience and liberation: a protest against state constraints on freedom within the city. Just as psychogeographers in the original Parisian Situationist vision of Guy Debord sought to discover astonishment on the terrain of the familiar by breaking out of the grooves of behaviour defined by capital, so politicized urban explorers present their trespasses as activism that ‘recod[es] people’s normalised relationships to city space’.

There are aspects of urban exploration that leave me deeply uneasy, and cannot be fended off by indemnifying gestures of self-awareness on the part of its practitioners.

hipster entitlement,

inattention towards those people whose working lives involve the construction, operation and maintenance – rather than the exploration – of these hidden structures of the city.

dandified nature of its photographic culture, which seems chiefly to refocus the problems of Caspar David Friedrich’s iconic 1818 painting, Wanderer above a Sea of Fog.

urban exploration’s awareness of the porosity of the city’s fabric, the proliferation of portals, rifts and drifts it perceived, and also its sense of sub-cities – like natural underlands – as spaces existing in long-term, slow-motion flux.

Cabinet of Mineralogy

Odessa catacombs. Odessa, like Paris, is a city built on limestone, and it contains the world’s most extensive sub-urban quarries. Some 1,500 miles of tunnel make up Odessa’s invisible city, sinking to a depth of 160 feet over three levels. I have seen maps of the Odessa labyrinth. More even than the Parisian network, it has the improvised appearance of an organism or organisms: the branching structure of coral, perhaps.

a film about exploring a few years ago, called Crack the Surface,

That cenote was understood by the local indigenous people to be an access point to the Mayan underworld, to Xibalba. In Mayan, Xibalba means “place of fear”. The whole limestone underworld of Mexico is a massively devotional terrain. Down there, where the water levels have risen, you sometimes swim past sunken altars, entrances to religious chambers that have been cut out of the stone.’

Xibalba

In the Mojave Desert, he accessed a boneyard of decommissioned aeroplanes: climbing over barbed wire to gain entry, then hiding in the landing gear of 747s and military cargo-carriers while security patrols passed by. ‘It was,’ he noted drily, ‘a vast playground and a long night.’

‘ghost stations’ of the London Underground

No security agency still steams open letters or reads people’s postcards; instead they watch text and WhatsApp conversations, and packet-sniff emails.

adrenaline, alcohol and extreme fatigue.

Generations of locals looking to dispose of their defunct vehicles without paying a scrappage fee had driven the cars up the hill and through the gap. The result was an avalanche of vehicles, a carchive, a slewing slope of wrecks that dropped into the chamber and continued into the black water as far as we could see.

These are trains above us, we are directly underneath the Métro and overground lines, and it is decades of train-judder that has left the ceiling unstable here.

the Jam’s ‘Going Underground’, growing in volume, booming down the tunnel.

Bowie’s ‘Underground’. ‘Ça c’est le cataboum!’

Bowie changes to ‘Underground’ by Ben Folds Five.

Over millions of years, the inland megacities of Delhi and Moscow will largely erode into sands and gravels, to be spread by wind and water into unreadable expanses of desert. The coastal cities of New York and Amsterdam, those claimed soonest by the rising sea levels, will be packed more carefully into soft-settling sediments. It is the invisible cities – the undercities – that will be preserved most cleanly, embedded as they already are within bedrock.

the doorway marked ‘Interdit d’entrer’.

The Lethe, the Styx, the Phlegethon, the Cocytus and the Acheron flow from the upper world into the underland – and all five converge in a welter of water at the dark heart of Hades.

The reason that classical literature runs with rivers dipping into darkness is geological: so much of the landscape in which that literature was lived and written is karstic in nature. Karst – from the Slovenian kras – is a topography formed by the dissolving of soluble rocks and minerals: principally limestone, but also dolomite, gypsum and others. Karst is vastly rich in its underlands – and it is also a terrain where water refuses to obey its usual courses of action. Karst hydrology is fabulously complex and imperfectly understood. In karst, springs rise from barren rock. Valleys are blind. A river can disappear in one place and appear in quite another, where it is given a new name by its new neighbours. Lakes appear that have no watercourse running into them and no watercourse running out of them – filled from beneath as the water table in the karst rises or drains according to season and weather (the ‘vanishing lakes’ described to the Royal Society of London in 1689 by Johann von Valvasor, a native of what is now Slovenia). Sinkholes and shafts pock karst landscapes like gaping mouths, making karst dangerous to traverse by night or in snow. Below the surface – if karst can be said to have a surface – aquifers fill and empty over centuries, there are labyrinths through which water circulates over millennia, there are caverns big as stadia, and there are buried rivers with cataracts, rapids and slow pools.

The distinctive topography of karst has developed its own distinctive languages of form and absence: a ‘doline’ (English) is a funnel-shaped sinkhole; an abîme or gouffre (French) is a water-worn shaft that can plunge thousands of feet; a cenote (Spanish) is a collapsed sinkhole, often flooded; an okna (Slovenian) is a point where water has worn a passage through rock that can be seen through, as if creating a ‘window’ in the stone.

Guizhou and Yunnan in China; the Nullarbor Plain of Australia; great areas of North America, including much of Florida; the Yucatan Peninsula in Mexico; the White Peak, the Mendips, the Yorkshire Dales and the Forest of Dean in England; the limestone gorges and highlands of central and southern France – these are all karst landscapes.

where the north-east of Italy borders Slovenia, there rises a long elevated plateau of limestone known in Italian just as Il Carso, the Karst. Far beneath the wind-scoured, sun-beaten rock of the Carso runs a river called the Reka in Slovenian and the Timavo in Italian – a river of rapids and meanders that in places flows more than 1,000 vertical feet below the light.

‘Metaphorically as well as geologically. There is much violence in the past of this region – and so little of it is spoken about. Rivers disappear and so do stories, only to rise again in unexpected places.’

Bees swim in the blossoms. I think of the strange lines Rilke wrote to the translator of his Elegies: ‘We are the bees of the invisible. Frenziedly we gather the honey of the visible, to gather it in the great golden hive of the invisible . . .’

the Romans declared an entrance to Hades nearby, at the point where the River Timavo dives underground at Škocjan.

‘We have cave systems here with living glaciers in them, we have caves containing an unmentionable species of blind orange beetles – the Anophthalmus hitleri, which is menaced by extinction because of its popularity with neo-Nazi collectors – and we have caves in which wine is left to rest with, it seems to me, mostly indifferent results.

There are symposia of earth tides held at Trieste University

The Adriatic glitters in the sky. ‘And perhaps above all we have the fascination, no, the obsession, with mapping the complete flow of the Timavo – which they sometimes call here the River of the Night.’

The Timavo rises as the Reka in pine forests on the southern side of Mount Snežnik, the Snow Mountain, on the border of Slovenia and Croatia. Its waters gather in the flat farmed valley land around Illirska Bistrica, and then wander, in idle half-mile loops, over impermeable flysch bedrock until, at the village of Škocjan, the flysch meets limestone and – in a geological conjuring trick – the Reka disappears.

The Reka-Timavo runs underground for around twenty-two miles before emerging again near Duino and debouching into the Adriatic

Škocjan canyon

There are a few places on the Carso plateau where it is possible to reach the starless river from the surface. Almost all of these access points involve serious caving. Almost all are ‘owned’ by differently aligned groups of explorers and cavers, who control local access to the Timavo, and whose relationship with its flow mixes cartography, adventure, science and a compulsive kind of dreamwork that would surely have fascinated Freud

However the Timavo is reached, the work of exploration is dangerous, difficult and dark. After heavy rain, the Timavo can flood at times up to 200 feet above typical height, killing anyone caught in a chamber or tunnel, or driving air under huge pressures up the shafts that drop to the river. Despite the efforts of the grottisti over more than two centuries, only around 15 per cent of the underground flow of the Timavo is presently known.

‘This is a Mithraeum – an underground temple devoted to the god Mithras,’ says Lucian. ‘Mithras was the god of the legionaries, little known in the pantheon and now hardly remembered, I think. He was born from rock – a true deity of the underworld in that sense – and the cult of his worship took place in subterranean spaces all over the empire. This was one of them, and it was probably used for more than 300 years, until it was abandoned around 400 AD. When they first excavated this place they found hundreds of coins and dozens of oil lamps and jars.’

Mithraism was a so-called mystery cult that spread across the Roman Empire from the first to fourth centuries CE, standing as a provocative counterpoint to early Christianity, which perceived in it a ‘diabolical counterfeit’ to their own emerging rituals. Its mysticism is itself mysterious, for so little survives in terms of sources to help us illuminate its beliefs and practices. What we know of it is largely reverse-engineered from the inscriptions and artworks found in Mithraic temples, and from the fleeting references that exist in classical literature.

Mithraism was an underground cult in several senses. Politically, it kept itself secret and out of view, its initiates greeting one another with encrypted signs of recognition. Theologically, it worshipped a god who had emerged from the rock itself. Topographically, its distinctive temples were almost all located below ground: the cellars of houses, natural caves or specially built vaults; sacred chambers known as spelea (caves) or crypta.

The Dark Star expeditions in Uzbekistan, exploring a system that may yield the deepest known cave, have been pioneered by female cavers, who cross subterranean lakes and rifts filled with blooms of blue ice. Female palaeoanthropologists have led the Rising Star expeditions in the Bloubank dolomites of South Africa, excavating early hominin burial sites. Each of these women has had to pass through an opening less than a foot wide in order to access the fossil remains, and the group has become known as the Underground Astronauts.

Two years after Loubens’s death, on 12 August 1954, a young Belgian priest called Jacques Attout volunteered to be lowered to the bottom of the Pierre Saint-Martin. Using a medicine chest as his altar, and with Norbert Casteret as his server, Attout celebrated Mass in memory of Loubens. He later recalled the service, in what has become among the most celebrated passages of caving literature for its convergence of theology and geology: Never again shall I celebrate such a Mass in a setting that was so closely united to the Divine Sacrament . . . In this vast cave we must have looked more like insects than human beings. And yet – our souls were on fire. We were so far from our surroundings, or if we sensed them at all it was because they had lost something of their material quality and become vast and luminous.

The Ario System is so extensive that its exploration requires expedition-style caving, where base camps and advance camps are established far underground as sites where equipment can be cached and sleep can be taken in tents – just as mountaineers attempting Everest move between successive camps while they gain height. Cave-diving skills are key to the Ario expeditions, for the further reaches of the system are flooded.

George Mallory famously answered the question of ‘Why climb Everest?’ with ‘Because it’s there.’ Extreme cavers jokingly modify Mallory’s answer when asked why they risk their lives for an ultra-deep cave system, with the words ‘Because it’s not there.’

The free-diver Natalia Molchanova similarly described her time below the surface as self-dissolving. Molchanova was one of the first people to free-dive the Blue Hole, a 390-foot-deep sinkhole in the Red Sea containing ‘the Arch’, an opening in the sinkhole’s wall that runs through to open ocean. More than a hundred free-divers and scuba divers have allegedly died in the Blue Hole, drawn into its depths by complex longings. Molchanova dived the Blue Hole on a single breath, safely: an astonishing achievement. But on an August day in 2015, she dived recreationally off the coast of Ibiza to between 100 and 130 feet – a shallow dive for someone of her rare abilities and experience. She did not resurface, and her body has never been recovered.

Budapest is built in part on limestone, and its invisible city contains both mine networks and cave systems caused by the upwelling of warm, dissolving water

‘Here,’ said Szabolcs at one point, ‘I am at peace within the rock.’

‘Allora,’ says Sergio. He is a man of few words, and most of those words, I learn, are allora: ‘now’, ‘let us begin’.

I cannot now say how long the descent took. An hour? Two? Time was irrelevant because there was nothing to keep it except for the hammer-beat of heart and the heaving of lungs.

We are terranauts and we have dropped through the roof of this chamber onto another planet – dropped into an underland desert of fine-grained black-gold sand. I shake my head in wonder and fear. Sergio stands quietly beside me. He has seen this place do this to people before.

The sound of this starless river is like none I have ever heard. It has volume. Its volume has hollowness. Each sound has its echo, and each echo its interior.

‘Conquistadors of the useless,’ Lionel Terray once called climbers – but this is another order of futility altogether.

Close to where the Timavo first plunges underground, we walk to Mušja jama, a 150-foot-deep fissure in the limestone into which more than a thousand Bronze and Iron Age artefacts were thrown over a period of around 400 years, from the twelfth to the eighth centuries BC. It is clear from the archaeological record that the fissure was a major sacred site, and that people came here from as far afield as central Italy and the Pannonian plain, bearing objects of power – socketed axes, spears, swords, helmets, drinking vessels – which were broken or burned before they were ritually cast into the abyss.

Nailed to the trunk of a beech near the lip of the sinkhole is a metal sheet, two feet or so high, and blotched with algae. Written on it in black ink is a long poem in Slovenian, entitled ‘Razčlovečenje’. At the bottom of the poem is scrawled the word ‘PAX’. ‘Its title means something like “Dehumanization”, or “Becoming Unhuman”,’ says Lucian quietly.

‘Doberdò is what I think in English is called a “turlough”,’ says Lucian, ‘an intermittent lake that wells up from underneath and within the rock when the rains come and the water level rises – but that drains dry in the summer months.’

The Isonzo runs bluer than any river I have ever seen. It is the blue of Cherenkov radiation, beautiful and chilling.

I have, again, a powerful sense of this landscape as one in which geology both produces and confirms ways of feeling. Here in this hollow terrain of the karst, historical memory behaves like flowing water, disappearing without warning, only to resurge under new names, in new places, with fresh force. Here in this topography of cavities and clandestine places, dark pasts get hidden, then brought to the light again.

We have entered a contested frontier region – part of the Julian March, the name given to the border zone of what are now Italy, Slovenia, Croatia and even Carinthia. Cultures and languages have mingled productively here, but this is also where groups perceiving themselves to be of different ethnic or national identities have visited appalling persecutions upon one another. Traces of conflict are still scored into the physical terrain (trenches, mass graves, monuments), archiving and perpetuating a modern human geography of violence and displacement.

Rivers are not meant to issue from the centre of cliffs. But then the earth is not meant to have tides, and mountains are not meant to have windows – and caves are not meant to grow glaciers.

‘This cave system is a mile in length, nearly 400 metres deep, and it perforates an entire mountain from one side to another,’ says Lucian. ‘The free movement of wind along the cave system, combined with the chill of the rock itself, keeps the temperatures within the system well below freezing. Snow gathers in the cave mouths in the winter, blown deep into it by the northerly winds, and – hey presto! – over thousands of years, the snow becomes a long thin glacier, winding within the mountain.’

Between 1941 and 1945 the limestone of southern central Europe – from the Cansiglio plateau below the Dolomites, across and down into what was then Yugoslavia – became the site of a brutal conflict. In April 1941, Yugoslavia was invaded by the Axis powers. It was captured and trisected, with Italy occupying southern Slovenia and Ljubljana, Hungary annexing the Prekmurje region, and Nazi Germany taking northern and eastern Slovenia. Germany and Italy soon began ethnic-cleansing activities in their new territories, deporting, resettling, driving out and killing thousands of Slovenes.

These anti-Fascist resistance groups – nicknamed ‘the woodchoppers’, and becoming increasingly left-wing in affiliation as the occupation continued, until formally declaring Communist alignment in March 1943 when they united with Tito’s partisan army – largely took the forests of the karst as their fortress and battleground. They fought nel bosco, in and with the woods.

The high karst was perfect for strike-and-retreat partisan tactics in occupied territory.

in the autumn of 1943, after the Italian surrender, and then during the notorious Quaranta Giorni, or Forty Days, of the Yugoslav administration of Trieste, following the fall of the city to New Zealand troops in early May 1945. During these terrible periods, geology and atrocity intersected: the landscape of the karst – which had served the partisans so well in terms of shelter and concealment – was repurposed for mass murder.

Sinkholes, caves, ravines and mineshafts throughout the limestone regions of Venezia Giulia and Istria became the locations of individual executions and group killings, carried out predominantly by Communist partisans but also by Fascist militias. Civilian and military victims were transported to the edges of sinkholes, and there were pushed alive, wounded or dead into these chasms in the limestone. In some cases, victims were bound to one another by barbed wire. Others were buried in scooped graves in the forests. The caves and glades of the karst filled with hundreds, perhaps thousands, of bodies. These extrajudicial killings are known today, especially by Italians, as the ‘ foibe massacres’ – from foiba, meaning a ‘sinkhole used for killing’. The bodies of those executed are still being disinterred in the shallow soils of deep woodland, or down in the sinkholes, where cavers will occasionally encounter human bones, bullets, rusting wire.

History itself possesses its own burials and exhumations. The history of the foibe killings is still today heavily contested, not least because for decades it was deeply submerged.

a politica sommersa, ‘submerged politics’.

The numbers and identities of those who died in foibe vary considerably, with the numbers given often depending on the political alignment of the researcher in question. In all cases, at stake is what Pamela Ballinger – in her major study of ‘the terrain of memory’ at the borders of the Balkans – refers to as ‘autochthonous . . . rights’, meaning the battle for the right to claim authentically to ‘belong’ to a given area of land, rock and soil.

the Elettra Sincrotrone, an international research centre that involves people from all the neighbouring countries and affiliations: it, too, is underground.

Grobišče Brezno za lesniko, the Wild Apple-Tree Shaft Grave.

Dehumanization But despite it all, they were people like you and me. Who are you? The living thrown into the madness, Killed with clubs and stabbed, Here crucified and no cross for you. But O, you humans, Your bones in the bottomless pit, They were people like you and me, Killed in the golden freedom. As you pass by, stop for a while, Think of your wrists bleeding in the dark night, Barbed wire wrapped around them, As they, cursing, goad you on, Beaten, naked, a corpse still living, You can hear the blows of the rifle butts, The screams, the groans, the terror turning into the sweetness Of approaching death. The fear, the pain, are vanishing, The footsteps echoing towards the void. In the bottomless pit countless numbers of them lie, But despite it all: they were people like you and me. PS: A curse be upon anyone who might attempt to erase this record.

The air brightens. The shadow past is shaped by everything that never happened. Invisible, it melts the present like rain through karst . . .

What had Anselm Kiefer written? I think there is no innocent landscape, that doesn’t exist

Dissonance is produced by any landscape that enchants in the present but has been a site of violence in the past. But to read such a place only for its dark histories is to disallow its possibilities for future life, to deny reparation or hope – and this is another kind of oppression.

Across the Dolomites and the Julians, retreating glaciers have begun to disclose their contents from the conflict a century earlier: rifles, crates of ammunition, unsent love letters, diaries and bodies. Two teenage Austrian soldiers have surfaced from a glacier in Trentino, lying top to toe beside one another, each with a bullet wound to the skull. Three Hapsburg soldiers melted out of an ice wall, hanging upside down near the peak of San Matteo at an altitude of 12,000 feet. The problem is not that things become buried deep in strata – but that they endure .

Isonzo

‘The Canin is a true karst peak. You can see how the limestone behaves differently. The type we’re on is more friable, sharper. The Canin is more of a bread loaf in outline, more like the moon in texture. You have to imagine it in cross-section, too. It’s honeycombed with natural cave systems. There are caves with their entry points on the slopes of the Canin that descend for almost two vertical kilometres.’ ‘A mountain has an inside,’ Nan Shepherd wrote in her great study of the Cairngorms, The Living Mountain, and it took me years to understand what she meant with respect to that granite range, which appears so outwards-facing

These are hollow mountains, lightless peaks, which everywhere turn in on themselves in the form of valleys and caves.

Eyal Weizman’s study of the landscape architecture of the Israel–Palestine conflict, Hollow Land, and its proposal of ‘elastic geography’, whereby space is to be understood not simply as the backdrop for actions of conflict, ‘but rather the medium that each . . . action seeks to challenge, transform or appropriate’. Weizman mapped the ‘elastic geography’ of the West Bank and Israel: the attempts made by erecting walls and fences hermetically to seal areas of territory, the nonsense made of such sealings by the tunnels that were dug under these barriers by Palestinians in order to smuggle people and weapons, and the arcs described by rockets fired out of Gaza by Hamas militants. He wrote of the reconceptualizations of space undertaken by both sides in the conflict: the way the disputed terrain ran vertically from the militarized airspace far above ground level, all the way down into the competition for control of the water aquifer that lies deep in the limestone, sunk thousands of feet below the West Bank.

We are the bees of the invisible . . .

The year is 1971 and a Soviet drilling rig squats on the sand of the Karakum Desert in Turkmenistan, near the village of Darvaza. Suddenly there is a crack, then a roar, and a disc of the desert floor 230 feet in diameter shatters and collapses into the abyss that opens beneath it, swallowing rock, sand and drilling rig in a few seconds. The void migrates to the surface . . . The drilling has punctured a natural-gas cavern, the cavern’s roof has collapsed, and now poisonous fumes are pouring into the upper world. The decision is taken to ignite the gas and burn it off. It is expected that this will take only a few weeks. More than four decades later, the pit is still on fire. It has become known as the ‘Door to Hell’ and ‘Hell’s Gate’. At night its orange flames light up the desert for miles around. People travel from around the world to approach its rim and sleep within the radius of its glow.

By some the mud volcano is seen as a consequence of corporate greed – an unnatural disaster. By others it is seen as an emanation of batin – of the submerged occult forces of the underland, of ghosts and spirits that dwell in the landscape and exist far beyond human bidding.

But the gleaming water – 45 billion gallons of it – is toxic because of the mining that has taken place here: highly acidic and contaminated with heavy metals. Thousands of the birds die and become a new surface, hundreds of floating acres of dead geese, dark-barred and white-winged, folded over one another in the pit.

Later, he develops the image. It should be an image of darkness. But down through the image falls a scatter of white points of dust, like static or a fine snowfall. These points are not dust, though – they are the imprints on the photosensitive film of pure energy, the radioactivity that was swarming invisibly around him in the Sarcophagus, swarming through him. They are the dazzling radio-autographs of uranium, plutonium and caesium – burning points of light that ghost the eye.

Later I will remember the days that followed mostly as metals. Silver of the pass. Iron of the bay and its clouds. Rare gold of the sky. Zinc of the storm in its full fury. Bronze and copper of the sea to the south as I escape.

Geology also has a role to play in the rarity of surviving northern-latitude painted cave art. Cave chambers form the most secure gallery sites for such art, and such chambers form most naturally in limestone: Lascaux, Chauvet, Altamira – all of the most celebrated prehistoric artworks were made in and on limestone. Limestone has the added curatorial power of often running a film of transparent calcium carbonate over wall paintings, which then sets and acts as a preservative varnish, mitigating degradation of the pigments. Northern Europe is sparser in limestone than Spain and France, though, and richer in igneous and metamorphic rocks. Where caves or overhangs form in such rock types, they do so by the erosive forces of ice or seawater and as such tend to be shallower and rougher-sided.

Alta in far northern Norway, where more than 6,000 images – predominantly petroglyphs – depicting reindeers, bears, humans, hunting scenes and the aurora borealis were made between c.7,000 and 2,000 years ago on glacier-polished rock.

One of the remotest of these painted caves lies near the western tip of the Lofoten archipelago: the island chain that extends for almost 100 miles into the Norwegian ocean at a latitude of around sixty-eight degrees. The cave’s modern name is Kollhellaren, which translates roughly as ‘Hole of Hell’, and it lies near the tip of the island of Moskenes, on its uninhabited north-western coast.

There are two ways to reach Kollhellaren. One way is on foot, over what is known as the Lofoten Wall – the precipitous ridge of peaks that runs down the centre of the island chain, and that in winter can be traversed only by means of a small number of passes. The other way is by boat, rounding the tip of the archipelago, and passing through the notorious Moskstraumen, one of the strongest whirlpool systems in the world, about which Edgar Allan Poe wrote his 1841 short story ‘A Descent into the Maelstrom’ – in which the whirlpool is figured as the portal of a tunnel leading to the core of the Earth. The Old Norse name for a maelstrom was bluntly pragmatic: havsvelg, ‘ocean-hole’ – a hollow in the sea into which everything flowed.

To reach and enter one of the painted caves of the Norwegian coast would have been a ‘rite of passage’ requiring ‘physical and mental ordeals’, writes Hein Bjerck, the archaeologist who discovered many of the painted caves

The ordeals were several in number: firstly the journey to the site of the cave itself, and secondly the passage into the cave, crossing its two key thresholds: first the entrance mouth, and then the point at which light fails and dark takes over. Bjerck writes of the challenging short-term visits made by the artists as ‘ritual actions’, journeys to ‘the outer fringe of the human world’. He notes, too, how the surviving names for cave-sites continue to emphasize their status either as performance space or as access point to a hostile other-world: Church-Cave, Hell’s Mouth, Hell’s Hole, Troll’s Eye.

The Troll’s Eye is a wave-smashed tunnel around 100 feet in diameter, running east-west wholly through the rock of a small island, in which the setting orange sun is framed once a year.

Of all archaeological specialisms, the study of prehistoric rock and cave art is among the most speculative. These acts of marking are irrefutable – but the immediate circumstances of their making are scarcely retrievable. It is hard to locate with confidence the intent or significance of individual artworks in wider webs of cultural practice.

the art of the painted caves of Norway is part of a circumpolar cultural presence left by the northern populations of Eurasia during what is now called the Bronze Age

Most of this art is located at liminal places – coastlines, riverbanks, caves; sites where, as Richard Bradley puts it in An Archaeology of Natural Places, ‘land meets sea’, darkness meets light, and worlds ‘come closest together’.

At Bohuslän – during the same centuries that the red dancers were being painted in the northern sea caves – a densely ritualized landscape was developed in a transitional site close to the coast. There, burial cairns were built in number on higher ground above the sea. Where bedrock was exposed, worn by glaciation to offer an ideal surface for inscription, hundreds of carvings were made. Hauntingly, many of these carvings are of footprints, which leave track-lines running down the angle of the rock into which they are cut. These ghostly prints – made by beings who are not present in any form other than the impress of their feet – seem therefore to record the passage of walkers from the barrow cemeteries on higher ground, down to the sea itself – as if spirits were leaving their tombs to make a final foot-journey to the domain of the deceased.

the Norse myth that the recently dead must be helped on their journey to the otherworld by the provision of ‘hel-shoes’ – specially cast soles that will allow the spirit to make its journey along ‘the path from the grave to the world beyond’.

The painted caves of northern Norway are all, also, clearly strong transitional sites. The presence in the painted caves of at least one figure wearing ceremonial headgear suggests possible relation with the three-tiered Saami cosmos, whereby the universe is arranged vertically into three layers – the sky, the earth and the underworld. Only shamans and the dead are able to pass between the tiers, by means of an axis mundi that – in the form of a river or tree – connects the upper and lower spirit realms to the living present of the middle realm.