This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

A 16th-century horror show built in a lovely Italian garden.

A church of bones, decorated with 40,000 human skeletons.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

Surprisingly Delicious Asian-Style Hot Dogs.

This Art Deco masterpiece has stood in for some of the most famous buildings in comic book history.

Plenty of old carney magic still haunts this photogenic amusement park.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

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

Stunning Roman aqueduct used for 1900 years and still standing.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

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

A landscape decorated with enormous skull sculptures.

Mysterious Spanish catacombs of unknown origins.

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

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

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

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

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.

Week-long block party becomes a competition for the best decorated street.

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

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.