A reproduction of the famous prehistoric cave paintings is hidden underground at the National Archaeological Museum.

This small museum tucked within a subway station holds pieces from Madrid's past.

This small and often-overlooked museum holds some of Spain's finest artistic treasures.

France's most famous cemetery, with some of its most curious tombs.

Indents in the pavement are all that remain from a grisly death machine in Paris.

This bridge was constructed from the rubble of the infamous Bastille.

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

This massive library holds what was once the largest book collection in the world.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

A surrealist timepiece by the artist of melting clocks.

Harry Potter once visited this massive limestone cliff, which was carved by an ancient glacial river.

An ocean in the making, in the Ethiopian desert.

A salt lake dotted with steaming limestone chimneys.

A Moroccan getaway in the mountain range that plays the Himalayas' stunt double.

Morocco's Argania trees are infested with nut-hungry goats.

A train station that was abandoned by the coal industry and was later converted into a cocktail bar.

A historic grist mill and active sluice on the Black River.

The highest point in New Jersey is marked by a massive, if simply named, obelisk.

Oldest existing wire suspension bridge in the United States.

This huge, disused viaduct is now a crumbling concrete underworld of covered in years of graffiti.