The secret city built by the Manhattan Project.

Ride the subways of yesteryear.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

All that's left of the quintessential "cabin in the woods."

The angel of death appears to weep black tears at this grave marker.

Tiki luxury on Nob Hill.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

This incredible collection of vintage pinball machines can be played at 25 cents a pop.

One person's lost luggage is another person's treasure.

Each year these high desert hills are absolutely covered with poppy flowers in a surreal show of nature.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

A hotel and restaurant serving as the mecca of kitsch.

New York City's smallest piece of private property.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

A self-built castle made by a mysterious man.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

Hollowed out cedar log tubs set in an ancient towering forest.

An abandoned facility that has become a place of ritualistic satanic worship, or so rumor has it.