Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

The Cold War-era "underground Pentagon" is a sprawling subterranean hideaway for the Defense Department.

This sprawling farm was once a Cold War-era hideaway for the nation's top diplomats.

These colossal desert barcodes have been fine-tuning spy satellites for decades.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

Portland had a unique approach to Cold War-era protections.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

One man's quest to collect artifacts from every aspect of human life has resulted in this eclectic Argentinian museum.

An intriguing antique iron Ferris wheel that most locals are sure was designed by Gustave Eiffel.

Carved fountains poignantly placed in parks and in front of special monuments.

A mysterious architectural gem in one of the most elegant areas of Buenos Aires.

From Nazi chemicals to the CIA, this architectural marvel has played a fascinating role in German history.

One of the Cemestos prefab homes built to secretly house thousands of Manhattan Project workers.

This eerie abandoned building with a dark history is said to be one of the most haunted places in the Philippines.

This tiny island featuring 9th-century Viking ruins is only accessible at low tide.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

Accessible only at low tide, the deserted island is dotted with World War II ruins.

In France, a medieval-style home pays homage to an intrepid explorer who discovered Québec.

Folklore and history carved into Brittany's coast.

A tiny church on a man-made island in the Adriatic.

Petrified footprints of one of the very first vertebrates to walk on land.

An ancient holy well said to be used by the patron saint of sailors and travelers, lost in the boggy west of Valentia Island.

An abandoned faux-pub made famous by a Guinness commercial.

The Avenue of Mausolea is a series of grand palatial tombs.