Catacombes de Paris

These underground tunnels date from the Roman period, when quarries were created to obtain building stone. Most sit at the base of Parisian hills like Montparnasse, Montrouge and Montsouris. In the late 18th-century, authorities began to use the caverns and tunnels to deposit bones exhumed from medieval cemeteries that had become unsanitary. During WWII, the catacombs were home to the French Resistance. Today, they're open to the public, who can view artfully arranged bones from years past. Miles of tunnels are still uncharted, but this 2km route, reached down a steep staircase, is well-lit and a constant 14°C. METRO: Denfert-Rochereau