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

Located more than 600 feet beneath sea level, this tunnel boasts the world's first undersea roundabout.

This park is home to California's first oil boomtown, with structures that have stood for more than a century.

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

A multi-storied adobe complex has been inhabited for more than a thousand years.

These aggressively sustainable art homes look like something out of 1970's science fiction.

An alchemist's "magic door" stands in the middle of a Roman park.

A reliquary of pop culture marvels, including the world's largest (and most terrifying) Jack-in-the-Box.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

Rusting away on the edge of New Jersey are the remains of a Cold War missile launch site.

An old-timey medicine shop that once served Chinese laborers during the Gold Rush is still open for business to this day.

The oldest operating apothecary in the US has treated everyone from Thomas Edison to Mark Twain.