The world's first and only natural nuclear reactor.

An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

This Quebec estate is home to the elaborate gardens of a self-taught horticulturist.

Sleep beneath the big screen at this old-school movie theater.

An abandoned water park overtaken by the dunes.

This simple apartment may have inspired some of the most important theories in the history of science.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

Charles Babbage's proto-computer, painstakingly brought to life.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

Western Europe's only representation of a Roman goddess still in its original location sits in an unassuming park.

The highest paved road in North America winds its way up Mount Blue Sky in Colorado to an altitude of 14,130 feet above sea level.

Michael Heizer's masterwork in the Nevada Basin.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

Sunset-colored dunes of volcanic ash make taking a poor photo impossible.

Potential high level nuclear waste storage site for the next 10,000 years and beyond.

Experience a charming 1930's version of "infotainment."

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

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

One of the largest, oldest, darkest, quietest motel rooms in the world.

This Cold War siren is one off the last of its kind still standing with its immensely powerful original horn.

A huge musical sculpture and other art installations on the National Oceanic and Atmospheric Administration grounds.

A rotting tree in the middle of Seattle doubles as an elaborately-controlled art piece.

A frozen relic of Seattle's hydroelectric boom is now a teaching facility for future engineers.