One of the largest ossuaries in Spain is packed from floor to ceiling with bones.

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.

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

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

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

This Funeral Hearse Museum represents the finest in cadaver transportation.

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

An architect transformed this abandoned cement factory into his castle-like workshop.

At the foot of a waterfall lies a peaceful swimming lagoon and evidence of over 60,000 years of human habitation.

A lush indoor jungle fills this bustling Madrid transportation hub.

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

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

A stately palace has been converted into the world's largest cannabis museum.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

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

Bacteria and algae give the salty water its bubblegum hue.

Wonderland replication in progress by one persistent man.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

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

An ancient Egyptian temple in the middle of Madrid, Spain.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

An unusual stroll through gentlemen's erotica demonstrates that pornography is timeless.

This cemetery features modernist statues as strange as its name.