Catacombs of Paris, France

Beneath Paris' City Streets, There's an Empire of Death Waiting for Tourists.

Let’s start from the beginning,

Between the 17th and 18th centuries cemeteries of Paris were getting so full that residue from decaying organic material was getting into the water supply and creating very unhealthy conditions., the number of dead bodies buried in Paris’s cemeteries and beneath its churches were so great that they began breaking through the walls of people's cellars and causing serious health concerns.

Louis XV (15) issued an edict banning all burials from occurring inside the capital, but because of Church pushback, which didn't want cemeteries disturbed or moved, nothing else was done. Louis XVI(16) , Louis XV's successor, continued the crusade, also proclaiming that all cemeteries should be moved outside of Paris. It wasn't until 1780, however, that anything was done. That year, a prolonged period of spring rain caused a wall around Les Innocents to collapse, spilling rotting corpses into a neighboring property. The city needed a better place to put its dead.

So it went to the tunnels, moving bones from the cemeteries five stories underground into Paris' former quarries. Cemeteries began to be emptied in 1786, beginning with Les Innocents. It took the city 12 years to move all the bones—from bodies numbering between 6 and 7 million -—into the catacombs. Some of the oldest date back as far as the Merovingian era, more than 1,200 years ago.

The Paris catacombs, then, are a 200-mile network of old caves, tunnels and quarries - and much of it is filled with the skulls and bones of the dead.

Despite the vast length of the tunneled, underground world, only a small section of it is open to the public. This tiny portion, known as Denfert-Rochereau Ossuary, or more popularly, "The Catacombs," has become one of the top tourist attractions in Paris.

Street names are etched into the walls to help explorers navigate their way around the underground version of the city and some groups have even been known to throw parties in the tunnels or drink wine. Visitors can also purchase audio guides, for 3 euros (about $4). The tunnels extend many more miles under the city, but it's illegal to visit most areas.

The tunnels are open from 10 a.m. to 5 p.m. Tuesday through Sunday, and cost around $11 for adults. Be sure to bring a jacket—the tunnels are chilly, with a constant temperature of 57° F.

There are, hence, more than 6million people underground. It is the reason there are few tall buildings in Paris; large foundations cannot be built because the catacombs are directly under the city's streets.