'I was stepping off subway platforms and running live tracks' – inside the strange world of underground addicts

Not long ago, on a muggy afternoon in the jungle of the Yucatán Peninsula, I switched on my headlamp and climbed through the rocky mouth of a cave.

As I moved from twilight into darkness, clambering over slimy boulders, I passed fragments of ancient Maya pottery on the floor. Hidden in one wall of the cave, I found a narrow crack, a horizontal slice in the rock. I shimmied through, flattening my body against the stone, before lowering myself into a large hidden chamber.

As I turned and angled my headlamp into the dark, I let out a long gasp.

I have spent the last decade travelling all over the world exploring subterranean spaces; not only caves, but nuclear bunkers and sewers, ancient tombs and subway tunnels.

My fascination with the underground – my life as a subterraneaphile – began when I was 16 years old and discovered an abandoned train tunnel that ran beneath my home in Providence, Rhode Island.

There was nothing remarkable about the tunnel – soupy puddles of mud, small stalactites on the ceiling – but for some reason it got under my skin. I’d go down all the time, sometimes with friends, sometimes alone, just to wander in the dark.

It was not until some years later, when I was living in New York, that I became aware of just how riven our world is with strange and fantastic hollows. Shortly after arriving in the city, I met a group of urban explorers, people who’d made a pastime of infiltrating the city’s hidden and off-limits spaces. Along with them, I started poking around in old tunnels, then strapping on boots and dropping into sewers.

Soon, I was stepping off the edges of subway platforms and running live tracks in the dark. I plastered my walls with maps of the city’s infrastructure. I never went anywhere without a flashlight. I loved the strange intimacy of exploring underground, of learning the city’s secrets. Beneath the city, I saw clandestine art galleries unseen by people on the surface, and met New Yorkers – so-called Mole People – who had been living underground for decades. It got to where the underground was all I thought about. I could barely walk down the street without stopping to peer into a sewer grate.

In the following years, as I began traveling to visit underground spaces in other parts of the world, I discovered an entire universe of subterraneaphiles. Everywhere I went, I encountered people who had become transfixed by the underground landscape and given their lives to exploring or making art or building in subterranean darkness. I trekked with a team of urban explorers through the catacombs and sewers of Paris, retracing the steps of the 19th-century photographer, Nadar, who spent months prowling the city’s underground, making pioneering photographs of spaces Parisians had never seen.

In London, I followed the work of the so-called “Mole Man of Hackney,” who, for reasons he could not quite express, spent three decades digging a warren of tunnels beneath his home. I met a farmer in Cappadocia, Turkey, who, while tilling his land one day, discovered an underground city – a sprawling, multi-level honeycomb of ancient tunnels – and now spent his days seated at the entrance, telling the story of his discovery to visitors from all over the world.

In the outback of Western Australia, I visited an Aboriginal family who had dedicated their lives to protecting their ancestors’ ancient sacred ochre mine, a deep blood-red pit in the earth, where people had been climbing underground to collect ochre for more than 30,000 years.

The truth is that all of us – our species, humankind – have always felt a quiet pull from the subterranean world. The underground may frighten us, it may repel us, but something has always drawn us into the dark. It is one of the deepest points in humanity’s shared heritage.

As I widened my search, I found cultures in every corner of the planet – from the ancient Greeks to the Lakota Native Americans to the San tribes of southern Africa – who held a profound and deeply-rooted connection to subterranean worlds. People who told myths and legends about the underground – stories of death and birth, demons and treasure, mystery and revelation – and who climbed deep into caves to conduct religious rituals, to commune with ancestral spirits. But the people I encountered who were most intimately connected to the underground were the ancient Maya, who once dwelled in the forest of the Yucatán Peninsula.

On that afternoon, in the hidden chamber of the cave, I found myself looking at the undisturbed remnants of a sacred ritual performed 1,000 years before. The entire floor of the chamber was man-made, constructed of soft dark loam brought underground from outside, and smoothed so flat you could dance on it. Embedded in the floor were skeletons of birds, pieces of jade and obsidian. At my feet, I saw charcoal ashes, fallen from ancient torches. In a clay statue, the spiraling grooves of an ancient thumbprint.

Underground: A Human History of the Worlds Beneath Our Feet by Will Hunt is published by Simon & Schuster at ￡16.99 and out now.