Folklore says this medieval fortress was plopped atop a portal to hell to trap the demons below.

This unusually shaped mountaintop tower looks like a UFO floating over the city.

A spiral staircase twists to the top of this unusual Czech lookout tower.

Walk through Czech history in Prague's largest graveyard.

An old asylum graveyard that's been abandoned for half a century attracts those seeking a dark thrill.

The world's greatest slide descends 18 stories from this looping mountaintop viewing platform.

Two monstrous faces loom over a village in Czechia.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

A beautiful Victorian-era cemetery, complete with a miniature village.

The often-overlooked ruins of one of the first buildings designed by famous landscape architect Frederick Olmsted.

Ralph Waldo Emerson spent two years living here decades before it became a Frederick Law Olmsted-designed park.

A Cold War secret surveillance tower used to spy on radio communications.

A former top secret nuclear fallout shelter now operates like a hotel stuck in the Cold War.

This network of conjoined cellars was riddled with traps and supposedly allowed the townspeople to pretend their homes were deserted.

Mummified monks and the accidentally interred, in a 17th-century crypt.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Bohemian paradise covered in majestic forests.

Thirty creepy ghosts now inhabit this decaying 14th-century church.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

The first museum in the world devoted to sexual gadgetry.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

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

Why have you never heard of the second most popular tourist site in New York?

An iconic steel and chrome diner from the 1940s left empty for nearly 20 years is in danger of being demolished.