The Hveragerði fissure runs through this unassuming shopping center.

The last remnants of a massive medieval wall that once encompassed the city of Berlin.

The signs of a long buried road can still be found hidden beneath a London sewer grate.

Home to items never before seen by the public.

A painfully obvious spy house sits right across the street from the Russian Embassy.

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

This study room in the New York Public Library saw the creation of one of contemporary America's greatest traitors.

These cinderblock farmhouses were actually World War II radar stations in disguise.

A museum dedicated to secret surveillance.

An exercise in radical design and social living that became the epicenter of Soviet spy networks in London.

The final resting place of the great escape artist, where some still gather to wait for his escape from death.

The author of Frankenstein is buried here, along with her parents and the heart of her husband, the poet Percy Bysshe Shelley.

Said to be one of Sweden's most haunted places, this vicarage once even attracted a ghost-busting priest.

This century-old grotesque has a mysterious history and may not actually be a rabbit.

World's smallest skyscraper, the product of a remarkable con.

A mysterious bridge over a sunken Roman road.

Peek into a cave of giant, glimmering crystals.

"Not too many people can say they've had a nuclear bomb dropped on them, not too many would want to." — Walter Gregg.

An eatery in a shallow river where diners can enjoy their meal mere feet from the base of an artificial waterfall.

An abandoned Soviet-era park that, when viewed from the air, looks like a pentagram.

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

The remains of a military communications outpost still stand on this Greek island.

An abandoned castle owned and ignored by Masons carries a cursed history.

The world's oldest hologram gallery and the labyrinthine laser laboratory of a holography pioneer.