Moorish signal station on a stratgic rocky outcrop.

Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft.

The people murdered during a 17th-century Norwegian witch hunt have been honored with a pair of stark, modern installations.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

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

This disused VLF radio station is no longer in service but the surrounding town still bears its name.

A war-torn Olympic relic is being overtaken by graffiti and nature.

Ruins of a late 1950s Polish ski jump ramp in the middle of the city.

This one-time health resort was used by aristocrats around the world.

Lavish royal estate punctuated with heated greenhouses.

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

Space-age monument to an early 20th-century uprising.

A Romanesque tower appears when water levels drop.

Located right outside of Vienna, visitors can take in expansive views of an ethereal forest.

A serpentine highway twists and turns over the treacherous Norwegian Sea.

An industrial relic is now one of Europe's most staggering art spaces.

Now an entertainment complex, the Lingotto building was once an avant-garde auto factory with a test track on the roof.

In memory of The Blur Building, the temporary exhibition pavilion of vaporous nothingness.

The university library shaped like a giant piece of Swiss cheese.

Yugoslavia's biggest underground airport lies in ruins.