The Catacombs of Paris: Underground City of the Dead

Many visitors to Paris don't realise as they walk the wide boulevards and explore the storied museums that there are over 300 kilometres of labyrinthine tunnels winding underneath the sprawling metropolis. Collectively known as the Paris Catacombs, it's what hides within this dark and otherworldly space that may come as a surprise. The Paris Catacombs contain Europe's largest ossuary – a space containing skeletal human remains. In fact, 20 metres beneath the sidewalks are the skulls and bones of over six million people. This morbid collection, assembled in the 18th and 19th centuries, has become one of the city's unlikeliest tourist attractions and a grisly draw to urban explorers keen to uncover a darker side to the City of Light.

The story behind the Paris Catacombs is as eerie as the bone-filled tunnels themselves. In the late 18th century, Paris had a problem. For hundreds of years, Parisians had relied on a few consecrated cemeteries within the city limits to inter the bodies of its departed citizens. Over time, these burial grounds became dangerously overcrowded, with many nearby residents complaining of noxious odours and unsanitary conditions. Finally, in 1780, after heavy rains, part of a wall surrounding the Cemetery of the Innocents collapsed, and corpses spilled out into the streets. After a thousand years of burials, it became clear that these overpopulated graveyards were a public health risk. A search began for a suitable place in which to relocate centuries worth of bones, and it was determined that the abandoned quarries outside the then city limits, in what is now southern Paris, would be the most suitable new resting place.

Worried that the Church and the pious Parisian population would be outraged at the removal of bones from consecrated land, the city government worked under cover of darkness to relocate the remains. From 1785 to 1787, priests were brought in to oversee the relocation of thousands of skeletons. The underground site was officially consecrated as the "Paris Municipal Ossuary" but became popularly known as the Catacombs of Paris.

The French Revolution brought the bone transfers to a halt, but they resumed in 1800 and continued on and off until 1860 as Paris underwent massive urban renovations throughout the 19th century. Once the dust settled, the bones of over six million people had been relocated from cemeteries throughout the city centre – some of them dating back over 1,200 years ago, to the Merovingian Dynasty. Although the bones were originally dumped haphazardly, during the Napoleonic era it was decided the bones should be organised into a necropolis resembling those found in ancient Rome. From 1810 to 1814, Inspector Héricart de Thury used a museographical and monumental approach to arrange the bones into intricate structures. Tibia and skulls were used to line the walls of the tunnels, and monuments in Antique and Egyptian styles were erected as decoration. Doric columns, tombs, steles and altars, all made of bones, line the macabre underground city. Thury also installed plaques featuring poetic and religious texts throughout the Catacombs, encouraging visitors to meditate on their own mortality. This concept, called memento mori (Latin for "remember you must die"), was popular in Medieval and Early Modern Europe, intended to remind the living to prepare for the afterlife.

Visitors to the Catacombs descend only 20 metres underground, but millions of years through geological time. Approximately 45 million years ago, Paris was covered by a tropical sea. The layers of mud and sediment left behind created a rich limestone layer that corresponds to the layer in which the Catacombs were dug. From Antiquity through to the Middle Ages, the quarries directly under the southern portion of the city supplied the stone used to build Parisian churches, castles and city walls, until a number of collapses occurred under Paris in the 18th century. The stone from the tunnels would eventually be used to create the majestic Haussmannian-style buildings that Paris is now famed for.

Over time, the Catacombs of Paris have become something of a cultural icon and a must-see attraction for all visitors to Paris. But the underground tunnels have a dark and dangerous side lurking in their maze-like depths.

The cataphiles are a mysterious subculture surrounding the Catacombs. This group of urban explorers has found alternate entrances to the Catacombs and mine tunnels all over the city and uses those unmarked doorways to gain access. Dark, damp and unmarked passages await those who venture into this dangerous territory. But despite the risks – and the fines for entering illegally – cataphiles have used the tunnels as backdrops for parties, concerts, cinema screenings, bars, dinner parties and a host of other activities, all frowned upon by the authorities.

Wherever skulls can be found, so can stories about mysterious happenings. Filled with the remains of so many people, there's no doubt that if there were such a thing as restless souls, they would be wandering through the Paris Catacombs.

One story concerns a doorman named Philibert Aspairt. During the French Revolution, Philibert was sent to the cellar to fetch a bottle of liquor. In the dark and crumbling cellar, he accidentally entered a door leading into the Catacombs and became lost as the light of his only candle flickered out. Philibert's body was found 11 years later, and it's now said that his ghost wanders the tunnels protecting lost cataphiles.

There's also the strange tale involving a group of police officers in 2004 who were exploring an inaccessible part of the Catacombs when they came across a recording of a dog barking, followed by a chamber that had been turned into a house with a bar, lounge, living room, workshop and 20-seat screening room, plus video cameras on the ceiling recording their every move. A few days later, when they returned to investigate, everything had been removed, and all that was left in its place was a note that read, "Don't search." Was it a cataphile hotspot? Or a home for wandering spirits?

Yet another legend has it that after midnight, the walls begin to talk as the voices of the millions of entombed Parisians lure unsuspecting visitors deeper into the dark. Perhaps this was the fate of poor Philibert?

In 1809, the Catacombs were first opened to the public by appointment only. Despite the creepy surroundings, visitors were morbidly fascinated by the underground attraction, and the tunnels were visited by kings and emperors alike. Nowadays, it's perfectly legal to enter the Paris Catacombs, and the annual number of visitors exceeds 550,000. A Catacombs tour with an audioguide, also available in English, takes approximately 45 minutes and includes walking 1.5 kilometres through narrow passageways with dim light. There are 131 steps down and 112 steps up, and a visit is not recommended for visitors with mobility issues, who suffer from claustrophobia or who may be disturbed by the sight of skeletons.

The Catacombs are located in the vibrant Montparnasse district on the Left Bank of the Seine. This bohemian neighbourhood known for leafy parks and foodie cafes is also home to a variety of excellent hotels, including the sleek Pullman Paris Montparnasse, only a 16-minute walk from the Catacombs, and the trendy ibis Styles Paris Maine Montparnasse, located a 14-minute walk away.

While not for the faint of heart, the Catacombs of Paris provide a fascinating and unique glimpse into the dark underworld of Parisian history.

• The Paris Catacombs location: 1, Avenue du Colonel Henri Rol-Tanguy, 75014 Paris (Place Denfert-Rochereau).
• Opening hours: Tuesday to Sunday, 9:45am-8:30pm (last entry 7:30 pm).
• The price for Paris Catacombs tickets is 29€ for adults, and 10€ for children ages 5-17. We recommend booking online for a fixed time slot in order to skip the lines (or to at least reduce your waiting time).
• Transport: Metro and RER B: Denfert-Rochereau; Bus: 38, 68.