Giant origami sculptures tucked into desert scenery beckon passers-by to explore further.

A hidden beach at the end of a tunnel of mangrove trees.

This ancient sinkhole-turned-healing-pool is a treasure trove of archeological discoveries and may even be the Fountain of Youth.

Prehistoric animals decorate this popular outdoor park.

The beautiful tunnel that ran from the lobby to Penn Station is still hidden underneath 34th Street.

Once an ambitious nature spa, these forest ruins now provide a serene monument to failure.

This concert pavilion on the shore of the Great Salt Lake has been destroyed by fire, water, and disinterest but keeps coming back.

An unfortunate geological resemblance to Satan has labeled this Pasadena gorge as a passage to the underworld.

The secret city built by the Manhattan Project.

This abandoned Navy base was transformed into an off-grid alternative living community for thousands of people.

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

Love, knishes, and best wishes from this legendary Lower East Side bakery.

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

The Grand Canyon of Texas.

An homage to everyone's favorite prehistoric cartoon family.

This spectacular track has run continuously since 1882.

An outdoor sculpture park of giant pink robots and post-apocalyptic Christmas scenes.

Nondescript elevator doors open to reveal a stunning, surreal world.

An abandoned relic of the city's failed experiment with below ground transit.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

A clear blue swimming hole with hidden caves, still unexplored.

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

Collapsing castle on the Hudson river was once the storage site of military surplus business.

After starting as a whimsical tourist attraction that eventually found its way to ruin, these renovated canals offer a lush and exotic locale on the Pacific Coast.