A once grand hotel now sits eerily abandoned in the Catalan countryside outside Barcelona.

Abandoned Nazi train station turned underground astroparticle laboratory.

Stunning Roman aqueduct used for 1900 years and still standing.

The abandoned ruins of a beautiful medieval castle just outside Barcelona.

The earliest known map to show America, discovered by accident at a Paris bookshop.

This awesome Spanish castle is so fantastical it was actually used on Game of Thrones.

A completely underwater art museum sends a stark message about humans' impact on the environment.

The morbid items in this small and hidden museum are not for the weak stomached.

The final resting place of the great navigator, or maybe his brother.

This house's itty bitty size means no humans allowed.

A whimsical brother of the nearby Fallen Angel statue takes the falling part quite literally.

This Navarrese cave's history of witchcraft and pagan ritual is not just embraced, but recreated each year.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

Giant eggs, walls of bread, and nightmare surreality mark the largest collection of works by Salvador Dalí.

A Spanish forest is filled with mysterious stone carvings.

A landscape decorated with enormous skull sculptures.

These magnificent city walls rise from the barren sun-baked Spanish plains like something straight out of a fairytale.

Commonly acknowledged as the only public monument to the Devil himself.

Turntable anonymously received orphans, alms, and groceries.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.

A museum dedicated to the Spanish occult in a town that was terrorized by the Inquisition.