A flooded Mexican cave that hides a river beneath the water.

Underwater art project will double as a massive artificial coral reef to help regenerate the damaged ecosystem.

An abandoned water sports stadium that has become a haven for graffiti and decay.

A community of collapsing homes more than a mile out from the Florida coast.

A rotting tree in the middle of Seattle doubles as an elaborately-controlled art piece.

An abandoned vacation home spent a decade taking on legends. It's now taking on water.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

Rusting, graffiti-covered tanks litter the beach of this island, once used by the U.S. military for target practice.

On a small Puerto Rican island, banks of secret naval bunkers lie abandoned and filled with piles of office equipment.

The world's brightest bioluminescent bay.

This small primate research island is teeming with playing, fighting wild monkeys.

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

The bat-covered home of one of the world's most popular brands of rum is located on a tropical Art Deco campus.

This niche museum devoted to ancient religious artifacts is shaped like the very thing it displays.

The highest peak in Puerto Rico is home to a rare fern that can only be found on six trees at its summit.

This limestone cave offers an incredible view of the Río Grande de Arecibo valley.

The world's second largest single-dish radio telescope, once used to contact E.T.

This former sugarcane transport tunnel is now a portal to a lovely beach.