The small cave that housed Tennessee's "first citizen."

A morbid secret lies hidden within the beautiful walls of the Boston Athenaeum.

A beautiful little museum hidden away in the heart of Barcelona holds a treasure trove of Ancient Egyptian artifacts

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

The "Jade Museum" is full of thousands of intricately carved works of art made from various precious stones.

This kitschy curio wonderland is full of fake animals, teak tables, and a cacophony of random bric-a-brac.

Located within a historic park, the beacon is the oldest standing structure in Miami.

Visit these gentle, bell-bottomed, exquisite equines at the home of North America's first Gypsy Vanner horses.

Once a year, at exactly 11:11 a.m., this monument comes to life.

More than five miles of underground passageways.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

A former Roman town that was once the home of Scipio Africanus.

The relics of dozens of martyrs are stored in a single chapel.

Jesus' footprints and the first catacombs in the world.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

St. Augustine's record-setting narrow street was designed to protect against pirates.

A remote desert lookout offers unparalleled views of the California badlands for those who brave the trek.

A 140-year-old castle with underground caves hidden in San Francisco.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.