A five-square-mile slice of Spain on the Mediterranean coast of North Africa.

This underwater graveyard commemorates a group of murdered 16th-century missionaries.

"Satisfying" is a good way to describe these beautifully aligned rows of Spanish mills.

This Arab fortress was once the largest citadel in Western Europe.

This mountaintop observatory is home to one of the world's largest reflective telescopes.

This chest hospital with a dark, haunted past serves as a fitting set for horror films and a paradise for ghost hunters.

Lava stone structures possibly dating back to the 19th century may have been a stopping point for voyagers between ancient Egypt and the Mayan Civilization.

This panoramic lift provides a futuristic ride up San Pedro Mountain.

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

The largest medieval water tank on the Iberian Peninsula is preserved beneath the Cáceres Museum.

This underground church is topped with a 500-foot cross that is seen by many as a beacon of fascist hubris.

A huge cathedral single-handedly constructed by one eccentric monk.

This huge abandoned fortress hidden inside a mountain holds a world of subterranean secrets.

A modernist church in an ancient village.

This 7,000-year-old megalithic wonder covered by a Franco-era reservoir emerges in times of drought.

Hundreds of caves once used to store grains and animal feed.

This influential Renaissance-era library was once the haunt of kings and monks.

Now a pile of ruins and rubble, this was a lovely mountain town as recently as 1960.

The atmospheric ruins of a historic church can be found on a hill above the city of Oviedo.

An abandoned Indian-inspired mansion.

A spectacular walk on the flank of a gorge.

A New York–based physician returned home to Spain to build his own elaborate monument to Christopher Columbus.

A network of hundreds of interconnected wineries in caves hides under the town center.

A well-restored ancient archaeology site gives a real feel for life during the Roman age.