A vault that holds six million dead people in Paris is a popular site to visitors. The Catacombs of Paris is an

The Catacombs of Paris are underground vaults in Paris, France, which hold the remains of more than six million people in a small part of the ancient Mines of Paris tunnel network. It is located south of the former city gate "Barrière d'Enfer" (Gate of Hell) beneath Rue de la Tombe-Issoire. The Catacombs of Paris was created when city officials had two concurrent problems. One is a series of cave-ins starting 1774, and the other is the overflowing cemeteries, mainly in Saint Innocents.

There were nightly processions of bones between 1786 and 1788 transferred remains from cemeteries to the reinforced tunnels, more remains were added in the later years. The Catacombs of Paris became a tourist attraction on a small scale from the early 19th century. It was open to the public on a regular basis starting 1874 with surface access from a building at Place Denfert-Rochereau in the extreme southern part of the city of Paris.

In 2004, Parisian police were tasked to do a training exercise in a previously unexplored part of the Catacombs of Paris beneath the Palais de Chaillot. They entered the catacombs through a drain and came across a sign that read Building site, no access. The police descended deeper into the tunnels and exposed a 400 square meter cavern with a fully equipped cinema. It included a giant cinema screen, projection equipment, chairs and a numerous of films, from film noir classics to recent thrillers.

Aside from this, in the next room, police exposed a fully loaded bar and restaurant, packed with tables and chairs. The discovery left police in confusion and amazement, not to mention the three phone lines and professional installation of electricity. The police came back three days later in the Catacombs of Paris with experts from the French Board of Electricity to figure out the source of the electricity. The cables had been cut and a note lying on the floor read, Do not try and find us.

Due to numerous incidents of vandalism and the theft of several skulls, the Catacombs of Paris were closed from October 2009 through December of the same year. With the reopening of the site comes also additional security tightening, reported, Atlas Obscura.