A crumbling hospital from the 1850s on Roosevelt Island.

A miniature golf course crafted inside the world's largest simulated cave.

It would take 35 firetrucks to fill this enormous glacial pothole.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

When the Austin Dam failed it destroyed much of Austin...and then it failed again.

In which a local geological marvel becomes a quaint roadside attraction.

Eccentric concrete mansion and museum designed and built by hand from the inside out.

Collection of trolley cars in the woods represent one man's attempt to preserve transportation history.

This abandoned Poconos resort is haunted by a history of kitschy romance and a violent fugitive.

These beautiful ruins deep in the Pennsylvania woods are thought to have been a ski lodge or a speakeasy, but no one really knows.

A beautiful oddities shop crammed with strange and morbid curiosities.

A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

Sail through this subterranean show cave that is home to a legend that would go on to name nearly everything around it.

Mysterious rocks that ring musically when struck.

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

An abandoned cemetery lies in ruins as the surrounding forest swallows it whole.

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

Rows of 19th-century brick ovens used to process coal into coke form the center of a wooded park.

A monument to a Native American leader who was known for never breaking a promise and met his end after signing a deal with white settlers.

Landmark dedicated to the plight of the American Indian in the 21st century.

The overgrown remains of an old rail bridge rise above the valley like ancient Greek ruins.

The ruins of the suspension bridge hang over Kingsbury Run as a ghost of racial prejudice.

This lovely university observatory continues to sit abandoned since its potential savior was sent to jail for fraud.

Faces carved into the cliffs create an otherworldly walking trail.