1.The Catacombs were built and conceived of in the late 18th century. Mass graveyards around Paris were overflowing, and so the bones were exhumed and arranged in the existing subterranean tunnels of the city's ancient quarry.
2.There, you'll find the bones of some 6 million Parisians.
3.You can also find graffiti dating all the way back to the French Revolution.
4.A portion of the Catacombs is open to the public, however there are dozens of secret entrances around Paris.
5.There are miles and miles of tunnels, not all of which has been mapped — getting lost if you enter illegally is a given unless you're with an experienced guide.
6.During WWII, the Resistance used portions of the Catacombs as hideouts.
7.Ironically, the Nazis also created bunkers in this underground city of death.
8.In more recent years, the Catacombs have become host to secret, underground parties. "Cataphiles" will tell you that there was at least one concert down there in 1817.
9.There's a legend about a guy who got lost and died down there in 1793. Philibert Aspairt's body was found 11 years after his death and it's said he was actually close to an exit.