An ethereal glowing blue ocean cave in Croatia.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

The birthplace of an eccentric alchemist and possible inspiration for the fictional reanimator of monsters.

Crystal clear lake with a shoreline of travertine located in a Colorado canyon.

A taste of the macabre Tokyo's ritzy shopping district.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

Northern Ireland's Brobdingnagian stepping stones.

Home of an evil witch famous within southern folklore.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

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

The first declared National Monument in the United States.

The haunting "Hell House Altar" is one of the few remnants of an abandoned college that has been a magnet for local legends.

Site of a former hidden treehouse in New Orleans.

Since 1874, this macabre collection has developed into a museum devoted to Scotland Yard's mementos of dastardly deeds.

Monasteries on rock pillars, once accessible only by frayed ropes.

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

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

Two stunning 17th-century libraries and a cabinet of curiosities.

Dodge prohibitionists and slide through the telephone booth in Crif Dogs.

Odd outsider art installations surround a Gold Rush-era ghost town.

Enormous lake at the bottom of a unique cave system.

The only structure left with direct ties to the Salem witchcraft trials of 1692.

A tiny microvalley etched into the side of Knocknarea Mountain hides another world.