Mine shafts and hard pastries await visitors at this massive mountain of salt.

Its appearance in "Game of Thrones" may spur on the long-awaited restoration of this medieval shipyard.

Rare karst landscape eroded from a flat seabed.

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

This former charity hospital for elderly clergy houses some of Seville’s most treasured paintings.

A site where “the ravages of the war are more striking…than any other place in contemporary Spain.”

A Romanesque tower appears when water levels drop.

Volcanic rocks ground down into sand make this Spanish beach as black as night.

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

Mysterious Spanish catacombs of unknown origins.

Stunning Roman aqueduct used for 1900 years and still standing.

Considered the birthplace of the Copper Age and Bronze Age, the river is tinted red from 5,000 years of mining.

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

Village situated on a narrow volcanic escarpment.

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.'

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

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

An enchanting monastery in the Spanish countryside appears lifted from a fantasy tale.

Wonderland replication in progress by one persistent man.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

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

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.