18th century anatomical amphitheater of the Royal College of Surgery of Barcelona.

A beautiful but toxic fountain of mercury.

This cemetery features modernist statues as strange as its name.

One of Europe's largest supercomputers is housed inside of a disused chapel.

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

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

The Gaudí-inspired building that was the start of Terrassenc modernism.

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

This medieval fortification has weathered the centuries better than any other structure from its era.

This ancient Spanish castle sits high upon a hilltop.

Tower that was a frequent stop on the travels of King James I.

Stunning Roman aqueduct used for 1900 years and still standing.

Archaeological site of Iberian people ruins.

A breathtaking canyon offers stunning views and frightful pathways through an ecological paradise.

Sanctuary on a ridge near an ancient shrine to a "Black Madonna" built by the founder of Opus Dei.

This religious complex carved into a cliff is steeped in legends of miraculous stags and the Holy Grail.

Eccentric sculpture garden brings Basque mythology to life.

Abandoned 18th century weapons factory in the Aezkoa Valley.

This narrow path was cut right into a French mountainside to feed the country's early naval expansion.

Abandoned Nazi train station turned underground astroparticle laboratory.

An arresting arch punched straight through a mountain provides one of the most scenic spots, and challenging climbs, on the planet.

A series of recreated fortifications mark George Orwell's path through the Spanish Civil War.

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