An extraordinary natural landscape of mountains, waterfalls, and rocky cliffs riddled with tunnels.

An enormous playhouse designed to look like 21 stacked Lego bricks, with another 25 million colorful Legos inside.

Air-raid tunnels hidden beneath this opulent hotel provided shelter and an escape route—and one of the world's longest slides.

These charming mailboxes became social media stars after a typhoon failed to topple them.

Enormous pendulum helps keep Taiwan's tallest building from swaying.

Home with Gothic windows featured in a famous painting.

This large pile of traveler-curated rocks by the dry lakebed is a longstanding tradition on the Old Mojave Road.

Where decommissioned airplanes and helicopters go to become part of Hollywood.

Everything you always wanted to know about borates is here.

For divers and music lovers, the Florida Keys' Underwater Music Festival provides the best of both worlds.

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

The secret city built by the Manhattan Project.

The remains of one of America's first radiation testing grounds still rest ominously in a Georgia forest.

This recently rediscovered Civil War-era submarine was the first to ever sink an enemy ship.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

A glimpse into the sacrifices of military members during World War II.

Hidden amid a collection of trails is the site of a tragic crash.

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

These eerie outliers of the lightning bug family glow a mysterious blue color.

This titanic steel chain linking two buildings was installed without permission but instantly beloved.

The sole remaining outpost of a once-thriving South Carolina chain still sells “pic-a-nic” baskets.

The first steel dam in the world and the only one still functional in the United States.

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

This huge dam across the Colorado River caused an armed standoff between two U.S. states.