Paris, France - The manhole looks like any other, covered by a cast iron plate on one of Paris' busy boulevards.
As a condition to taking reporters below ground, its exact local must remain secret. One furtive look around to check for any sign of the police and a local guide lifts the plate and ushers onlookers down the hole, quickly shutting it behind him. Seconds later the group hits ground in complete darkness, the sound of cars and pedestrians above muffled as they enter the bowels of Paris.
Franck, who goes by the nickname "H2O" underground, is a long-time "cataphile", an urban explorer of the ancient tunnels and caves known as the catacombs of Paris. He didn't want his last name published.
The guide knows his way around most of the 300-kilometre network dug under the city. Some tunnels run directly under the main streets. Some are closed off with brick walls to stop cataphiles from pursuing their illegal explorations.
Facing one such wall, Franck aims his flashlight towards a hole on the side that is just wide enough for a human body. "My friends and I dug this passage," he explains.
'Silence keeps you awake'
Anyone can visit the historic underground cemetery known as the catacombs of Paris. Bones and skulls of around six million Parisians were transferred to the ossuary in the 18th century, after a series of public cemetery closures.
Wandering beyond the guided tour, however, is strictly forbidden. The quarries were dug over several centuries to gather the rock that would go on to make cathedrals, churches and the city's ramparts. Twenty-one metres below ground and with millions of tonnes of rock above, the catacombs are no place for claustrophobes.
The first time you spend the night here, silence keeps you awake
There is no phone network, no light and no help. Lose track of your whereabouts and you may wait days to meet another soul. Aside from headlights and the sound of voices, the corridors are pitch black and the silence deafening, even for experienced explorers. "The first time you spend the night here, silence keeps you awake," the guide explains. "The sound of your own heartbeat and the shush of air coming through your lungs can be overwhelming."
The catacombs have attracted Parisians looking for adventure as far back as urban legends go. Weekend adventurers and would-be holders of a great Parisian tradition cross paths below ground to share a meal, party and sometimes spend several days away from their hectic lives at the surface.
At the height of its popularity in the 1970s, the catacombs were the site of large drug-induced parties that caught the attention of authorities, which in turn made access more difficult. But it hasn't kept fans away. Franck has been coming down here since 1992. He even met his wife underground. "She still comes down sometimes," he says "for important parties."
Cruising around the tunnels has become trickier with times. Hardcore cataphiles use stealth and good home improvement tools to defy the city's regular attempts to keep them out of the quarries. Two years ago, the main entrance was barricaded overnight.
Recently, an unusual access to the quarries was closed off by city workers. "It's the fault of those who used it in broad daylight," wrote one cataphile online the following day. "We had fun while it lasted," wrote another. They had discovered the entry point just months ago and had kept the secret amongst a handful of friends.
The cat-and-mouse game continues with the police, adequately nicknamed " cataflics" (catacomb cops), making regular visits to catch urban explorers in the act. "They are putting themselves in danger," a police official explained over the phone, "because many of them get lost." An underground run-in with the cataflics will set unlucky travelers back €60 ($83).
It is easy to see why underground exploration is prohibited: any drastic transformation to the structure of the tunnels could threaten the city's foundations. Disaster struck in the 18th century, when whole building blocks collapsed into the empty tunnels below. As a result, King Louis the 16th created a special quarries unit to this day responsible for keeping the tunnels structurally sound.
"You can tell which walls have been reinforced, and which will need to be consolidated in years to come," Franck explains, pointing to a crack in the rock above our heads. Deterioration of the site is also an issue.
"There are considerate and there are bad cataphiles," explains Gilles Thomas, an underground expert and author or The Catacombs of Paris. When he discovered the site in the 70s, he was delighted by small engravings carved by illustrious 19th century engineer, Henri Pointaré. "Now most of them are covered with graffiti," he says.
In times of troubles cataphiles are a close-knit group. When he fell down an empty well and broke his leg, Franck's friends helped him back to the surface. And when he tried to exit a manhole after an exhausting expedition, only to find that a motorbike was parked on top of it, "a friend of mine and I tried to force the plate open," he recalls. They eventually found another way out.
Many catacombs fans are wary of showing the passageways to outsiders. "Some of us would like the catacombs to remain a small private club," Franck confesses. In the circle, everyone goes by a nickname, communicating on forums to share information about flooded or unsound tunnels and run-ins with the cataflics.
Clueless visitors, however, are those cataphiles most want to keep away. Such as the Italian tourists Franck once ran into. They had set off on their own, relying entirely on a miniature map of Paris, the kind available for free in the Galeries Lafayette shopping mall. "They also showed me a map of the subway," he recalls. "Amateurs give the place a bad name when they get lost and teams must be sent down to find them."
An electrician by trade, Franck continues to visits the catacombs for the friends he makes underground. "I may find myself sharing a meal with a street cleaner, a student, an entrepreneur and an insurance consultant, " he explains. "I can't tell any of them apart. When you're covered in mud, social barriers disappear."