A stunning, abandoned limestone quarry in southern Indiana provided the stone to erect the Empire State Building.

An alternate history park where the Union Army loses the war... to dinosaurs.

This woodland architectural installation acts as a camera obscura for the heavens.

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

The only remnant of a small mining town is an abandoned railroad tunnel that is steeped in ghostly lore.

An enormous natural sandstone bridge in Kentucky.

The longest navigable underground river in the United States is home to countless blind and albino animals.

The only freestanding table rock formation east of the Mississippi.

A castle built by an eccentric medieval enthusiast in rural Ohio.

River pirates, murderous bandits, and serial killers used this Illinois cave as their debauched hideout.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

America's post-nuclear-attack chambers of Congress.

The remnants of the fortress that saved Georgia from the Spanish still stand guard on their swampy island.

A retired tobacco farmer's pet project turned into a sturdy miniature city.

Hikers can still stroll beneath the long conveyer of this abandoned mining facility hidden in a West Virginia river gorge.

One day a year it is legal to jump off of this astoundingly tall bridge that spans an Appalachian gorge.

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

Charleston's historic city jail once held everyone from pirates to Civil War POWs.

Oldest unrestored plantation house in America that is open to the public.

The only Florida state park with publicly accessible caves.

A six-foot pair of socks hangs from a drawer of the world's largest bureau.

This modern castle sat empty for decades before a fire inspired its builders to complete its luxury halls.

The highest point in Virginia can only be reached by passing through ponies and flowers.

The world's longest known cave system.