Abandoned blockhouses from Nazi Germany's Atlantic Wall erode into the sea on a French beach.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

A 14th century bridge built as a fortress, where the devil lurks on one of its towers.

Small French town or alien garage?

Holy Grotto of Montserrat Monastery holds one of Europe's mysterious black Madonnas.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

An architect transformed this abandoned cement factory into his castle-like workshop.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

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

At the foot of a waterfall lies a peaceful swimming lagoon and evidence of over 60,000 years of human habitation.