This quirky little private museum is home to more than a thousand stones, carved by nature, that resemble human faces.

Inside the columbarium, thousands of colorful, high-tech Buddhas guard the ashes of the dead.

This curious fresh and salt water lake holds a secret that draws in deep divers from around the world.

The world's longest tunnel with an undersea section.

Flames have been burning within this mountain for more than 2,500 years.

The most southern point you can drive to in the Western Hemisphere.

This retro underwater observation tower would make the perfect lair for a sea-loving villain.

The conquistador's former fortress is the oldest preserved colonial building in the Americas.

Climb atop one of the world's longest and heaviest trains for an unbelievable journey across the Sahara Desert.

This strange sculpture of a menacing skull surrounded by sun rays was discovered at the foot of the Pyramid of the Sun.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A nostalgic bibliographic gem.

A derelict bit of transportation infrastructure hidden in the woods.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

The United States Capitol's former columns still stand.

Erected in 1697 this Philadelphia bridge is the oldest surviving roadway bridge and perhaps the oldest stone bridge in the United States.

One of the oldest of its kind.

This meticulously extracted nervous system allegedly came from a 19th-century custodian who donated her body to science.

Yo, Adrian!

Tour the dark and beloved poet's former cobwebbed basement, which may have inspired "The Black Cat."

Where America's first doomsday cult awaited the end of the world.

World's first "penitentiary," meant to be humane, drove men insane.