The oldest public library in Ireland.

This whimsical stacked cabin looks like something out of a children's book.

Human-made caves excavated to hide a secret society of wealthy pagans.

This nearly abandoned "company town" is a ghost of Puerto Rico's once-lucrative sugar industry.

This Roman quarry once held secret masses and smuggler's contraband and is now home to rare species of bats.

An Italian hillside ghost town.

Abandoned cemetery of the former Psychiatric Hospital of Volterra.

This former fascist summer camp was abandoned for decades.

This entire town moved to a safe location after it was devastated by an earthquake, but the remains of the original town are still around.

During World War II, this rice mill became a Nazi concentration camp.

These pools have been abandoned for over 20 years.

A line of abandoned, alien-like fortresses dot the mountains of North Italy.

The now-abandoned Fascist summer colony served a dark purpose during World War II.

A domed disco abandoned since the '70s now attracts artists and explorers under its unique roof.

This amazingly preserved Doric temple was abandoned before it was ever completed.

This overgrown mountain village has been abandoned for nearly a century.

Italian director Pier Paolo Pasolini fell in love with this lonely 13th-century tower while making his most famous film.

The ruins of a medieval village that was abandoned after a 19th-century inferno.

An abandoned bell tower in the middle of nowhere is the last testimony of a forgotten medieval village.

Stare out over the lagoon and beyond from this 10th-century campanile on the island where the city of Venice began.

An abandoned 17th-century baroque hunting lodge with a wonderfully strange architectural plan.

Built to be the ideal penitentiary, this abandoned panopticon saw several revolts and even a prisoners' coup.

The abandoned ruins of a failed resort hide on this verdant, picture-perfect island.

A fascist-era rural village abandoned since the early 1980s.