The Catacombs of Paris

This subterranean ossuary holds the remains of a staggering 6 million people. Beginning in around the 10th century the city of Paris began to look for ways to deal with overflowing cemeteries, but it wasn't until the late 18th century that a solution was found. Abandoned stone quarries near what is now Place Denfert Rochereau were opened up and the tunnels were filled with the bones of the dead. Later priests arranged the bones and skulls into ghastly sculptures and arrangements. The visit takes about 45 minutes and covers 2km, a maximum of 200 people are allowed into the tunnels at any given time.