A lush indoor jungle fills this bustling Madrid transportation hub.

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

An iconic photograph from the Spanish Civil War saved this shrapnel-scarred historic house from destruction.

The mysterious large white cross visible from the runway is a memorial to a massacre during Spanish Civil War.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

This abandoned viewing platform has become a monument to unnecessary government spending.

This architectural oddity is an oasis of green on the outskirts of Valencia.

Beautiful tiles decorate many of the town's surfaces and stand testimony to its glorious artistic history.

This ancient fort has been a great insight into the Roman presence in the region.

A hidden treasure of an abandoned city lies deep in the jungles of Campeche, Mexico.

An ancient system of freshwater caves filled with animal bones, including that of species long-extinct.

A magical sinkhole on the Yucatán Peninsula is adorned with mini waterfalls and hanging vines.

This abandoned island off the Venetian coast has been a radical monastery, a political prison, and a secret Nazi base.

The plague quarantine island home to the alleged "Vampire of Venice."

One of the last Depression-era bandshells still standing was the site of Elvis Presley’s first live concert.

This Memphis recording studio launched the careers of Jerry Lee Lewis, Johnny Cash, and Elvis Presley.

This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The underground sanctuary of a mysterious ancient cult.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This bridge is haunted by the ghost of a distraught mother.