A playground inspired by differential calculus dangles from the ceiling of the Liberty Science Center.

This unassuming retro burger joint was billed as “diner of the future” at the 1939 World's Fair.

Now abandoned, the first public health hospital in the U.S. saw more than one million immigrants from around the world.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

One man's lifelong obsession with death.

The final resting place of many of New Jersey's most famous residents, including U.S. history's most in-vogue antagonist, Aaron Burr.

This metal disk commemorates the birth of a historic American holiday.

A vertical tube that allows you to see what's going on underneath the Antarctic sea ice.

An eerie smiling woman looms above the granite tombstones.

More than a century after her death, Little Gracie Watson remains one of Savannah's most often-visited residents.

This haunting tombstone comes complete with a heartbreaking story of love and loss.

This secluded walking trail is a hidden gem of a Pittsburgh park.

One man's attempt to create an artistic wonder on a run-down block in Detroit.

Find out what it sounds like when doves cry at Prince's recording studio estate turned museum.

This artist's home turned gallery/museum preserves the creator's love of "Eastern" influences.

The remains of a Canadian train crash are now mouldering beneath layers of rust and graffiti.

On the side of a remote mountain, a stone face bearing an inscription of mysterious origin.

Wedding chapel's mysterious spiral staircase said to be miraculously constructed.

A discreet little stairway on St. Nicholas Avenue leads to a quaint and unexpected cobblestone street of 19th century wooden rowhouses.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

The world's largest occupied bat houses hold hundreds of thousands of flying mammals.

This massive subterranean fissure is known as the "underground Grand Canyon."

Four abandoned towers hidden above the Douglas fir forest in Washington.

A prime example of New Orleans' unique architecture these early 20th century homes were built to look like steamboats.