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

An enormous concrete structure built over a nuclear crater.

The largest man-made crater in the U.S. marks the spot where we once tested mining with nukes.

The contents of this safe survived a 37-kiloton nuclear bomb.

This largely forgotten piece of Cold War history stands hidden in the woods just north of the Mississippi Gulf Coast.

On October 26, 1963, a 12-kiloton nuclear device was detonated here in granite some 1,211 feet below the ground surface.

A facility built in 1992 for an underground nuclear test remains in place today.

Hide from the tourist hordes in these relatively unknown, and unguarded lava caves.

In 2018, Pohoiki Road was severed by lava flowing from the eruption of Kilauea.

In 1329, Christine Carpenter entered this small stone cell in the hopes of becoming a living saint.

Artist Scott Hocking took a dilapidated 1890s barn to create his massive "Barnboat."

Located in the world's highest-altitude Dark Sky Community, this observatory welcomes amateur and professional astronomers alike.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

One man's dream has turned into this naturally growing chapel made of almost nothing but trees.

The oldest covered railroad bridge still standing in the United States.

This 12-seat movie theater is the smallest in the world.

This groundbreaking 16th-century map is known as "America's birth certificate."

Smallest house in Toronto sits on a lot meant to be just wide enough for cars to drive through.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

Walk down these stairs to get an underwater view of Switzerland's Lake Zug.

The final resting place of the world's first nuclear reactor.

To get to or from this Canadian ghost town, you'll need to cross 11 single-lane bridges.

In 1909, the steepest and most difficult piece of track on the Canadian Pacific Railway was replaced with a series of spiralling tunnels cut into the mountains.

This jagged colossus of a building is mostly held together by an enormous concrete exoskeleton.