Abandoned tunnels dug for the once-thriving sea salt industry on the coast of southern Spain.

A daily pyrotechnic celebration marks a beloved tradition during Valencia's festival season.

Despite its grandiose name, this enigmatic first-century void under the town is no cave, and it's possibly not a palace either.

Hidden well off the beaten path in Catalonia is this crumbling medieval castle that is slowly being covered in graffiti.

The ruins of a bombed medieval village memorialize the destruction of the Spanish Civil War.

Among the oldest structures in Madrid, these Moorish walls once guarded the medieval city of Mayrit.

Abandoned 18th century weapons factory in the Aezkoa Valley.

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 macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

An outsider folly near Madrid.

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

An impressive display of ships and artifacts from the ancient Mediterranean maritime trade.

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

Remarkably intact Roman stone fortifications have encircled this Spanish city for centuries.

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

A display of torture devices used in the Spanish Inquisition and other scourges of medieval Europe.

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

On La Gomera, "Silbadors" communicate in a 4,000-word language of whistles.

An eccentric collection of antique items shares space with a prop-quality witchcraft museum.

This cafe offers a curated collection of treats and tipples made by monks and nuns.

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

This magical space partly designed by Antoni Gaudi is one of the best examples of romantic gardening in the Mediterranean.

This ancient Spanish castle sits high upon a hilltop.

Famed architect Antoni Gaudi built this generous thank you gift to a friendly host who housed him during a job.