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

Rare karst landscape eroded from a flat seabed.

Of course Salvador Dalí lived in a castle...

The world's largest wooden structure.

Stunning Roman aqueduct used for 1900 years and still standing.

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

Cliffside houses provide a spectacular view from their perch above the valley.

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

An isolated village literally built into the crevices and rock formations of a mountain.

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

Giant eggs, walls of bread, and nightmare surreality mark the largest collection of works by Salvador Dalí.

This cemetery features modernist statues as strange as its name.

A beautiful but toxic fountain of mercury.

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

The medieval town's star-shaped walls are geometrically dazzling, though not entirely impenetrable.

Europe's largest collection of matchbox designs is a fascinating exploration of the cultural history of the world.

Pagan monument converted to Christianity with the population.

Men in rubber-soled boots serve as your "brakes" on this toboggan ride Hemingway described as "exhilarating."

A cluster of granite granaries perched on stilts.

Elaborate tile work in this railway station tells the story of Portugal.

Located in the thermoelectric factory that once powered the entire city, this Portuguese museum is shockingly fascinating.

"Portugal's Stonehenge" is made up of nut-like stones aligned with the heavens.

One of the largest Roman settlements in Portugal.

An abandoned mine now resembles a post-apocalyptic landscape of derelict buildings and blood-red pools of water.