An explosion of natural color known as "the river that ran away from paradise."

Roman ruins top white travertine terraces formed by ancient hot springs.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

Natural time capsule containing an alien ecosystem.

Geothermal waterfalls in Tuscany.

An emerald-green grotto just a short trip from Austin.

These mammoth-yet-narrow crevasses in the Earth are perfect for taking an otherworldly swim.

Intensely colorful calcite pools in Southern China.

Iceland's largest lagoon is home to stunning multi-colored icebergs.

Moss and stone turn this waterfall into an otherworldly liquid veil.

Medicinal spa created with the discharge from a geothermal energy plant.

A popular swimming hole that hides one of America's most deadly diving spots.

The mystery of this small, brick pond eluded its possibly only investigator until his death.

This natural Icelandic fissure allows divers to swim right between two volatile tectonic plates.

This small town in the Netherlands has no roads but instead, miles of canals and over 100 bridges.

This tiered waterfall is so pretty it may cause visitors to cry tears of their own.

This natural sea cave hides a small wonderland of natural turquoise beauty.

A magically clear, blue river that seems to spring from nowhere.

This ultra-modern wooden boardwalk turns the ocean into a swimming pool.

A lovers' beach, tucked below the surface of the island, provides a safe haven for romance.

Each year melting snow turns these Austrian hiking trails into scuba zones.

An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood.

A magical sinkhole on the Yucatán Peninsula is adorned with mini waterfalls and hanging vines.

Stay in a room with a view... of the bottom of the ocean.