I was already 10 feet up the 20-foot ladder, drain water crashing down on my face, my silt-caked hands slipping for grip on the rungs, before I realised that the top end was only secured in place by a thin little loop of chain. But I kept climbing. It felt like one of those trust exercises – where you switch off your instinctive self-defence mechanisms to instead fall blind into someone else’s arms. Reaching the top of the subterranean waterfall, I stepped off the ladder into a wide, concrete-walled chamber – the entrance to the network nicknamed ‘G.O.D. Drain’ – where two separate storm drains converged before pouring their contents over the edge and down towards the creek. One wall was covered in white paint, upon which was drawn a grid that formed a guestbook, signed by all the people who’d made that same climb before me. They never saw me, but somehow, reaching this point, it felt like a group hug.

When I spent a summer in Australia, back in 2013, I explored a dozen different storm drains beneath Melbourne. Many of these waterways started their lives as freshwater streams, but when the city developed they were boxed in, culverted, then in many cases eventually buried, redirected underground to form a network of veins under the streets. In some cases I explored them with friends but even when I was alone down there, there was always a sense of community that permeated those tunnels. They were alive with voices – in the guestbooks, the stickers, the graffiti that alternately pranked or welcomed new explorers: one horrendous looking shaft, narrow enough to trap you and clogged in foul-smelling sludge, was labelled “free hugs this way”; while in another drain, a welcoming painted text read: “Hello to adventurers who come to places like this.”

On many of these subterranean sorties I was walking (or wading) in the footsteps of the Cave Clan. Formed in 1986 by three then-teenagers – Woody, Dougo and Sloth – the group grew, began opening chapters in other Australian cities, and would achieve an almost mythical reputation over the years, becoming the subject of media outrage and fascination, while being lauded by others as pioneers in the modern trend for recreational urban trespass. From drain to drain, I saw the tags left by Cave Clan members dating back as early as the ’80s. We shared all the same emotions in the same places – curiosity and wonder, claustrophobia and relief – just never together.

It felt like a kind of archeology, like I was chasing the ghosts of someone else’s childhood. Or perhaps I was the ghost… a future echo in the tunnels, a shadow just beyond the light of the campfire. Feeding on the afterimage of emotions.

In Welsh, the word hiraeth describes a feeling of deep longing for a place or a landscape, perhaps even for places which were never more than a myth or an idea. (When I asked a Welsh friend about it, she said “the coastline, the mountains, even the rain – are as much a part of you as your heart, lungs and bones. So when you feel hiraeth you really do feel it with every cell in your body.”)

The German word sehnsucht achieves something similar, though more abstract: a bittersweet yearning for some unknown joy. The regret that we no longer remember what it was that we once longed for. The Journal of Research in Personality defines sehnsucht as the emotional ambiguity arising from a reflection on unfinished or imperfect aspects of one’s life, and the desire for ideal yet unattainable alternative experiences. In the lyrics of Pink Floyd:

When I was a child I caught a fleeting glimpse,
Out of the corner of my eye.
I turned to look but it was gone.
I cannot put my finger on it now.
The child is grown, the dream is gone.

There was a bingo hall in the town where I grew up. They had an over-18s policy, I don’t know why, as it was just a few dozen elderly folks sat on the rowed seats of a former cinema, crossing numbers off cards as a big ball-spinning machine rattled away on the stage. One time a friend and I snuck in there. We must have been about 10, and literally the only exciting thing about it was that we weren’t supposed to be there. There was no one at the door, and we spied on the hall from the cloakroom until someone spotted us – whereupon we ran to the toilets and hid in a cubicle. An elderly man, with a mixture of frustration and bewilderment, had to knock on the door and ask us to kindly leave.

A few years later there was a fire in the house immediately behind the hall. The bingo nights stopped, the old building was condemned, and it wouldn’t be long before the whole site was cleared for redevelopment – glassy, modern residential units popping up in its place. But for one whole summer in my early teenage years, the building was left abandoned. So on one hot June day, myself, that same friend, and two others, parked up our bikes and then climbed over the wall that circled the neighbouring house’s garden, then we hopped the dividing wall, to land in bushes beside the old cinema.

Although years had passed since I last saw inside, the interior looked as though the bingo players had all just stepped out for a minute. A calendar of events was pinned to the wall, open to the month and year of its closure. The bingo machine was still on the stage, and numbered balls lay scattered beneath the rows of cinema seats. I brushed against the seats as I reached for a ball to take as a souvenir: up close, the red velvet upholstery smelled of damp and mould.

At the back end of the hall, on the upper floor, in what was once a projection booth, we found evidence that someone had been living here. There was a mattress on the floor, with blankets, empty water bottles and an ash tray. An old brown telephone was plugged into the wall, its cable trailing halfway across the floor to reach the bed. The thing that most caught our attention though, was the wall full of newspaper clippings. They were pinned above the bed, whole pages or little squares of paper, all of them featuring stories about people with physical deformities. We never did find out who had been living there.

After the cinema, we went out back and into the house where the fire had started. It sat right in the middle of the block, surrounded on all sides by newer street-facing houses, and garden walls. In the middle of the building, the largest space, where the master bedroom was situated directly above the living room, the dividing floor had burned through completely to create one huge, corrupted, double-height room. It felt like a dark reflection of the cinema hall – cavernous, black and organic. We stayed there a while, poking and turning the charred remains of a home. I remember a yellow phonebook, covered in a pattern of burns that looked like barbecue grill marks. In the small bedroom upstairs we found a teddy bear, half his fur melted and one eye missing.

The four of us who shared that experience, we were really close for a few summers – we even started a band – but not long after we all went in completely different directions. One got married young and became a responsible adult (I heard he has kids now, and manages a restaurant). Another is in prison. The third stuck with the music, and eventually had his big break: now he plays lead guitar in a relatively successful touring metal band. Meanwhile I’m doing… whatever the hell it is I’m doing these days.

We had no concept of time, there was only the present. But I feel a kind of wistful sadness when I think back to those summer adventures now. I felt it again just recently, triggered by an unexpectedly poignant line in the series finale of The Office, when Andy Bernard says: “I wish there was a way to know you’re in the good old days before you’ve actually left them.”

This was how I felt while exploring drains in Melbourne. Climbing those ladders, ducking through tunnels, and poking around in the artefacts of subterranean parties that all ended long ago… facing the darkness to emerge on the other side into the comforting embrace of congratulatory graffiti tags, written decades earlier for someone else, and yet feeling as though they were speaking to me directly. It was like looking at someone else’s photo albums and feeling a warm glow as you imagine yourself in them.

I got to know the names of specific explorers… or sometimes I just recognised their handwriting. Upstream in G.O.D. Drain, the passages got gradually tighter and smaller the further we hiked from the waterfall at the creek; the interesting landmarks grew fewer, and looking at my watch to see it was already early evening, I began to think about turning around. Then I saw scribbles on the wall – the same authors that welcomed me into the drain earlier were also sharing my concerns here: “The end is not nigh,” said one. “Time to head back,” read another, and I agreed.

Another summer, a Russian friend gave me a tour of the subterranean Neglinnaya River that runs under Moscow, and later I’d read an account of a similar expedition written by Vladimir Alekseyevich Gilyarovsky, a journalist and occasional drain-explorer working at the start of the 20th century. The place he described had barely changed in all that time, the same bricks and rats and water, oblivious to the surface city above. There is a feeling as though time functions differently underground; as if all those graffiti tags, those expedition accounts, were not happening decades or centuries apart, but were parallel slices of reality, concurrent adventures, connected by the aura of shared emotion.

The work of Stephen King gives me that same sort of nostalgia: in The Body (later adapted for film as Stand By Me), the four children who hike down the river looking for the body of a missing boy… or It, with its preoccupation with abandoned houses and sewers. There’s that feeling of stumbling across dark spots in the overlooked peripheral spaces of day-to-day life. The edgelands and underlands of suburbia. I always got the impression that King wrote from experience, as though his childhood might have looked a little bit like mine. Reading those books on the school bus, I used to think that the 12-year-old Stephen King might have been a fun friend to explore drains with.

I started running tours in Ukraine in 2016. There are some incredible spaces under Kyiv – they have natural underground rivers, and then there’s an ingenious section of drains that zigzag down a hillside, designed in part to alleviate the risk of landslides, with slits between the concrete panels that allow it to collect moisture out of the soil and channel it away towards the Dnieper River. You can walk through sections that are over a century old, tsarist-era red brick drains, then step suddenly into vast, Soviet-era concrete tubes that look like leftovers from a metro project. I take tour groups into the drains of Kyiv, and on those days, I bring in a local guide. He’s a young guy who spent his teenage years exploring these tunnels, knows them like the back of his hand, and as we leave the circle of daylight behind and march single-file through knee-deep water into the under-city, he reassures the group that he’s been exploring storm drains for seven years now. In the darkness I do a quick calculation and realise that my first drain was over a quarter-century ago – before this guide was born. I say nothing, but suddenly I feel very old.

(And now I feel older still, considering how recent events have relegated the very phenomenon of Ukrainian tourism circa-2016 to the status of “the good old days.”)

I was around 8 years old when I first went drain exploring. I was in the cub scouts, and one afternoon we were learning camping tricks in the woods at the edge of town. The scout leader told us to bring tin cans from home. We cleaned them and put little candles inside to make hot plates, then we made batter out of flour and milk and butter, and cooked tiny pancakes on them that we ate with blackberries from the hedgerows. Later we’d make a campfire and cook bread over it on sticks. At that age though, I got distracted very easily. When I went to wash my hands in the stream I found the gaping concrete entrance to a storm drain… it was big enough that I barely needed to duck as I instinctively hopped inside to investigate. Apparently my disappearance gave the adults quite a scare. They were close to calling the police by the time I popped out again, covered head to foot in slime and cobwebs.

I had a taste for it after that, but growing up in rural England there just wasn’t that much in the way of urban structures to explore. The occasional drain… but mostly farm ruins and abandoned houses. I had friends who enjoyed this stuff too, but none of them were quite as keen as I was. That’s part of the reason I was always so fascinated by the diggers in Moscow, or the stalkers who navigate the ruins and re-wilded landscapes of the Chernobyl Exclusion Zone in Ukraine. This is not some detached, journalistic interest for me – rather it’s because I know, had I grown up there with the Zone at my backdoor, I would have been one of them.

Similarly in Melbourne, exploring that extraordinary labyrinth of storm drains running right the way beneath the city, and reading through the tags and comments left over from decades of subterranean adventures, a sprawling, literal and metaphorical subculture… when I was in my teens I could only have dreamed of having access to that kind of world.

When I got home from Australia, I wrote a few articles about exploring the Melbourne drains. I did a piece on the ANZAC Drain, where the Cave Clan have their annual gatherings, and another one on Maze Drain – a real obstacle course of a tunnel where I had the misfortune (or stupidity) to crawl headfirst through a nest of highly venomous redback spiders. I wrote an article about the Melbourne drains for Atlas Obscura too.

I got a lot of emails from Australians in the months after that. Many were just asking for the co-ordinates of drain entrances, but other messages came from experienced explorers. I heard from a couple of Cave Clan members, who offered to give me a tour the next time I visited (and I still mean to take them up on it some day). One of those people I became quite friendly with, and we chatted online often… until he died in a drain not long after. From what I understood from secondhand sources, it happened in a storm drain close to his home, a place he’d been many times and knew inside out. He was exploring on his own that day, and it was just stupid luck – he slipped on mud, banged his head, and drowned face-down in a few inches of water.

People still email me now asking for tips on how to get inside those drains, but usually, I have to disappoint them. I just couldn’t bear to have it on my conscience if anything went wrong.

In 2014, after one of my articles about Melbourne drains went semi-viral, an Australian radio station invited me on for an interview. I had never done radio before and decided to give it a shot. It was a disaster though, like we were talking completely different languages. The host – a bright, bubbly, chatty personality – asked me what it felt like to explore the huge network of drains under Melbourne. I think she was ideally looking for a one-word answer. Awesome! or Creepy! or Cool! would probably have sufficed. But instead I got thinking about those graffiti tags, about the friends I explored with but would never meet, and about the bittersweet feeling of discovering your greatest childhood adventure twenty years too late… of idealising someone else’s childhood, but then knowing also that by now it’s an illusion for them too, and that real life has happened in between, and that none of us can ever really go back to that feeling again.

“Hello?” the host nudged, with an awkward laugh. “Are you still with us?” After a long uncomfortable pause, I think the best I could manage was something like It’s complicated. We don’t exactly have a word for it in English.