The deeply creepy cat­a­combs are a net­work of old quar­ry tun­nels beneath Paris and the final rest­ing place of around six mil­lion Parisians. Most are anony­mous skulls and bones tak­en from the city’s over­crowd­ed grave­yards dur­ing the eigh­teenth and nine­teenth cen­turies. It wasn’t until the author­i­ties realised its poten­tial as a tourist attrac­tion that the bones were arranged in the macabre dis­plays seen today.