"The Paris Catacombs are truly spooky, with the remains of more than six million people located throughout the vast system of underground tunnels. While you can tour some of the tunnels today, be warned, as they're not for the faint of heart. And don't even think of venturing down there after midnight. According to urban legend, that's when strange voices (supposedly belonging to those who are buried there) will try to convince you to wander deeper and deeper within the tunnels until you get lost." - Travel + Leisure Editors