The Catacombs, in Denfert-Rochereau, are a labyrinth of quarried tunnels - the final resting place of six million Parisians whose bodies were moved here from overcrowded graves in 1810. Visitors can explore the eerie bone-lined passages, 18 metres underground.
These dank subterranean passages filled with spooky bones and macabre quotations carved into the stone are not for the faint-hearted. About two kilometres of the passages are open to the public - the way is marked with spotlights and the walk takes around 45 minutes.
The rest is a vast network of underground passages where you wouldn't like to get lost unaccompanied, so don't leave the path! Take a coat with you even in summer, as it's quite chilly underground.