These magnificent city walls rise from the barren sun-baked Spanish plains like something straight out of a fairytale.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

This Navarrese cave's history of witchcraft and pagan ritual is not just embraced, but recreated each year.

A lush indoor jungle fills this bustling Madrid transportation hub.

Commonly acknowledged as the only public monument to the Devil himself.

An ancient Egyptian temple in the middle of Madrid, Spain.

Mountain where Jesus was first tempted by the Devil.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

This 11th-century castle sits so low you can't see it behind the surrounding buildings.

A 'living museum' in Leiden, the oldest of its kind in the Netherlands.

A nuclear reactor created for Eisenhower's "Atoms for Peace" campaign is now used for research at a Dutch university.

This centuries-old gothic monster has been converted into a sprawling, glossy bookstore.

This still-celebrated home was a radical architectural experiment in 3D De Stijl.

An art installation memorializing a tram stop, which became a tram stop.

Old ships and machinery fill a historic harbor in the city that's home to Europe's largest port.

Rotterdammers' dirty minds gave this santa a dirty nickname and cursed it to a life of wandering.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

This bird-loving brewery is situated in an old municipal bathhouse, nestled beside a 300-year-old windmill.