The highest peak in mainland Spain is said to be the final resting place of a Muslim king.

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

An abandoned socialist utopia built in the late 19th century.

A fiery-red region of scooped out land still largely untouched by civilization, tourists or otherwise.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

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

These striking ruins of a castle resemble a ship's stern.

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

This abandoned naval battery stood at the ready as recently as the 1980s.

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

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.

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

A contemporary art installation housed within a Gothic cathedral.

Haunted tuberculosis hospital built by the patients.

An abandoned Indian-inspired mansion.

12th-century holy complex shares land with a natural park full of heavenly waterfalls and raptors.

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

This century-old ruined temple was reborn as "The Church of Skate."

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

Visit a surreal landscape so otherworldly NASA actually used it to train the Apollo 17 crew.

A charming Spanish village sits atop this natural limestone overpass.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

An ancient Roman theatre restored to its former glory in the Spanish city of Cartegena.