Abandoned medieval hill town.

The ruins stand as a somber reminder of France’s worst civil catastrophe of the 20th century.

This mosque was based on Sub-Saharan Islamic architecture and created for the Senegalese Tirailleurs.

From carts to cars, this leftover Roman bridge in France has managed to survive for centuries.

These medieval ruins have survived since the 12th century, even providing shelter from the Nazis.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

Half a century after it was abandoned, this ghost town is coming back to life.

A well-preserved medieval village nested on a rocky outcrop and surrounded by a network of cliffs, natural bridges and canyons.

The deserted pirate-themed restaurant still entices explorers.

Historic medieval fortified city in southwest France.

A functioning Roman-era aqueduct and bridge in rural southwest France.

This castle-fortress is a living example of the transition from medieval defenses to modern fortifications.

Village situated on a narrow volcanic escarpment.

Religious dwelling in a Spanish volcano.

A Romanesque tower appears when water levels drop.

Abandoned waterpark turned counter-culture mecca.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

Hidden well off the beaten path in Catalonia is this crumbling medieval castle that is slowly being covered in graffiti.

This medieval fortification has weathered the centuries better than any other structure from its era.

Cursed swimming pool left abandoned is now a favorite of filmmakers and ghost hunters.

Abandoned 18th century weapons factory in the Aezkoa Valley.

A Franco-era dam flooded (almost) everyone out of this centuries-old Aragonese town.

The deserted remains of a luxury hotel turned hospital ward.

Locals use these rock pools and waterfalls for swimming and cliff diving.