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

An unnatural lake in a naturally beautiful setting.

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

Drift through underground caves on a tube.

The world's brightest bioluminescent bay.

On this Puerto Rican island, many abandoned naval ammunition bunkers sit open while a few have been padlocked by locals as personal storage.

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

Fascinating military history, awe-inspiring wildlife encounters, and endless outdoor adventures draw people to this sprawling park.

A luxuriant botanical garden below sea level.

History is hiding at the Morean Center for Clay.

Loyal fans of one television's most famous painters still come to pay their respects.

Meet manatees face-to-face at this zoo for native species.

Manatees congregate around a power plant's discharge canal where the water is especially warm.

A tiny, unassuming park in Tampa that belongs to the Republic of Cuba.

Hidden in the plaza next to a pizza shop is an amazing little oddities shop.

Visitors to this shop will find fossils, minerals, meteorites, skeletons, oddities, and much more.

A home built with marble tombstones from the graves of 2,200 Union soldiers buried in a Virginia cemetery.

America's first public mental health facility.

Twisted girders are all that remain of an Icelandic bridge that was wiped out by a combination of volcanic heat and glacial floods.

This black church sits alone among a field of lava rock.

An isolated, rusty phone booth commemorates Iceland's first international telegraph cable.

The oldest steel ship in Iceland has been beached for years and is now a rusting ruin.

This elegant arc of a waterfall marks a religious turning point.

The bright red stripes streaking across the rocks are the star feature at this Icelandic waterfall.