The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

Board a mine car and descend the #190 slope 300 feet underground into the Clark Vein of coal.

Once the world's largest reinforced concrete structure, this abandoned bridge now beckons urban explorers.

This park contains a number of standing stones meant to heal and inspire.

A tour de force of a fountain, memorializing a man who loved fountains more than anything else.

A daily replay of the experiment that proved the rotation of the Earth.

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

The castle still holds traces of the abandoned Roman fort it was built atop.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Tucked behind New Jersey's abandoned Gingerbread Castle lie the eerie ruins of a once-flourishing paper mill.

One of the oldest of its kind.

This elaborate towering structure was once famed for its revolutionary height.

The fastest transatlantic ocean liner sat abandoned in a Philadelphia shipyard for decades.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

The famous bell was secreted away and hidden in a church in Allentown during the British occupation of Philadelphia.

The remains of a community that was forced to move for a dam that never materialized still rot in this Pennsylvania park.

A tunnel once abandoned now thrives with graffiti art as an off-limits makeshift gallery.

Oldest existing church in New York and the inspiration for Washington Irving's "The Legend of Sleepy Hollow."

This disastrous New Jersey safari park saw animal attacks, escapes, and disease before being abandoned.

This mouldering abandoned mental hospital was once a center for progressive healing.

Vacant Beaux-Arts buildings that serve as reminders of a beach town’s glory days.

A train station that was abandoned by the coal industry and converted into a cocktail bar. Now it’s home to the local visitor bureau.

Buildings that dynamite couldn't bring down were abandoned because of bathroom issues.

A toxic ghost town sitting atop a massive coal fire.