Inside the Paris Catacombs (photograph by Claire Narkissos)

“Just a leisurely stroll around the Empire of the Dead,” I told myself when a friend got wind of a private expedition through a forbidden section of the Paris catacombs. At night.

I didn’t think too deeply about what that might entail, happy to forgo a long queue in the cold outside Denfert-Rochereau’s carefully maintained public face of the sprawling Paris ossuary.

With construction commencing during the 1780s in disused quarries as a solution to the irksome sanitation problem of overcrowded cemeteries, the catacombs comprise a 321 kilometer (nearly 200 mile) labyrinth of caves and tunnels housing the remains of six million people — half the population of the City of Lights thriving directly above.

Catacombs Tunnel (photograph by Claire Narkissos)

A “cataphile” is not somebody with a loyalty card for the Café des Chats, but a passionné who frequently makes the journey between the worlds of the living and the dead. In doing so, they risk being caught by a police task force charged with patrolling underground. Some devotees make amateur maps to distribute within an exclusive community, some dig their way into hidden sections; others organise secret film nights or even flame-throwers’ parties, turning these subterranean dungeons into their personal playground. Some respect the space; others don’t.

My group of six dreadlocked cataphiles were of the respectful variety, not leaving so much as a cigarette butt or breadcrumb behind during the five-hour visit. (Yes, we ate down there.) They came well prepared for our descent, I noticed as I glanced at the amateur photographer strapping on her thigh-high military combat boots, then looked down sheepishly at my own rainbow sneakers and yoga pants.

From our rendezvous at the 14th arrondissement Alésia metro, we scrambled down to an abandoned railway and marched along the track until the group leader (who prefers not to be named) pointed to a mud-slicked hole in the ground. My heart sank a little when it became apparent that I would be spending most of the evening wading down narrow passageways up to my knees in cold, cloudy-brown water, squeezing my way through ominous openings.

One of the makeshift tables in the catacombs (photograph by Claire Narkissos)

Maybe turn back here if you’re claustrophobic or squeamish about getting dirty. Still, it was with a convivial spring in our step that we greeted and passed other groups of explorers along the seemingly endless rocky corridors, leading to chambers equipped with stone tables and benches. We ripped into the supply of baguettes and beer, pointing headlamps under our chins to tell jokes and ghost stories — a strange yet comforting camaraderie. Sometimes we ceased all clowning to commune with the profound silence that enfolded us, a floor-to-ceiling graffitied Spongebob looming over us like Hades.

Unlike the restored two kilometer segment of the catacombs accessible to the public, where bones line the passageways in patterned formations, most of the têtes de mort laid to rest here have been stolen, our “guide” explained. I was just starting to feel disappointed when we were ushered through a crawlspace; suddenly I found myself on my hands and knees atop a sea of femurs, some brightly painted and set upright as macabre totems, and the occasional brainpan, which my comrades pointed out would have made ideal ashtrays. We went from a cavernous “auditorium” thick with film-themed graffiti to what appeared to be an eerie shrine for a young girl departed too soon; a flawlessly pretty teenager smiled up at us from a photograph placed next to a preserved rat floating inside a beaker.

Underground Paris (photograph by Claire Narkissos)

I got nervous each time our guide, who has been exploring the catacombs since he was a teenager, stopped in his tracks to look at the map — the Paris street names directly above us are etched onto the walls — or herded us back the way we came after taking a wrong turn. We piped reggae and French rap through mobile phone speakers to keep energy levels high, facilitate a swift exit, and avoid getting separated, at last clambering out just before midnight. On a whim, we decided on a different route back to civilization, jumped a stone parapet, and narrowly missed the flics, whom we later discovered had begun their vigil at our original entry point.

I shook bone-dust out of my hair, the only non-dreadlocked explorer in the group. It felt good to take in the crisp, cool air. And even better to take a bath.