The secret city built by the Manhattan Project.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

South Carolina's last remaining slavery auction house is now a museum devoted to its own tragic history.

A unique museum dedicated to the Gullah-Geechee people, housed within an old oyster cannery.

In the late 1990s, a mechanic and fan bought this iconic sportscar back from the dead.

This is one really big nut.

The highest point in Texas is capped by a big silver pyramid.

Decades of discarded bottle caps line this alleyway, a fixture of Texas A&M.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

An emerald-green grotto just a short trip from Austin.

This playground sculpture of an icon from the past is dedicated to the children of the future.

After this former brothel closed, its interior remained almost frozen in time.

A French chateau, failed utopian community, odd museum, and Stonehenge replica in rural Washington State.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

The only Native American museum along the Oregon Trail, run by the peoples who have lived on the land for generations.

Sweet Willy, at 30 feet tall, is the world's biggest beagle.

A haunted hot springs hotel that went from healing retreat to asylum before it was restored.

One of the most remote spots in America and the first protected wilderness area in Nevada, named after an old legend.

Life-sized sculpture of a blue whale made of hand-recycled plastic trash.

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

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

When ecosystems collide in the arid Southwest.

Rippling sand dunes frozen in the Arizona rock.

One man has installed bathtubs into the Utah desert floor to harness the powers of a natural hot spring.