A 19th-century subterranean reservoir repurposed as a contemporary art cave.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

This awesome Spanish castle is so fantastical it was actually used on Game of Thrones.

The final resting place of the great navigator, or maybe his brother.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

"Alleys of Stone" form natural mazes in Spanish natural park.

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

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

A landscape decorated with enormous skull sculptures.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

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

A museum dedicated to the Spanish occult in a town that was terrorized by the Inquisition.

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

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

A beautiful but toxic fountain of mercury.

This semi-secret storybook hedge maze is also the oldest garden in the city.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

The studio of Catalonia's most famous theatrical designer remains exactly as he left it.

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 vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

This cemetery features modernist statues as strange as its name.

This Funeral Hearse Museum represents the finest in cadaver transportation.