An earthwork sculpture built by Robert Smithson in the Great Salt Lake only reemerges during drought.

Vortex-shaped aquarium hosts Europe's largest school of piranhas and other ocean creatures.

A turquoise lake within a volcanic crater.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

Fantastically decorated underground chambers built in the 1760s.

Unparalleled stargazing, one of Colombia's best observatories, and a swimming pool can all be found in the middle of this ancient tropical forest.

Monument to a brutal, ineffectual US bombing campaign and a sobering reminder of the human cost of the Vietnam War.

Carvings in Turkey's Marble Road may have directed ancient Romans to a hidden brothel.

Disney World's very first waterpark is now an abandoned ruin being reclaimed by the swamp.

On the Oregon coast there is a natural hole that seems to be draining the sea.

This geothermal hot spring hides beneath a slowly growing mineral dome.

One man has installed bathtubs into the Utah desert floor to harness the powers of a natural hot spring.

The small cave that housed Tennessee's "first citizen."

Bell tower juts out from a village buried under a lake.

A Romanesque tower appears when water levels drop.

This cluster of little wooden huts once ground local farmers’ wheat into flour during the days of the Austro-Hungarian Empire.

This volcanic cave lake is essentially hard proof that Iceland is the most magical place on Earth.

This natural French spring has been turned into a magical grotto by Roman and medieval constructions.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

Boats must transform into railroad cars to navigate this Polish canal.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

Hidden deep in the Guatemalan jungle is a turquoise paradise of natural pools, caves, and waterfalls.