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

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

This extraordinary geological oddity resembles human-made pavement.

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

Futuristic apartment blocks are the backdrop for Montreal surfers hangin' ten on the Habitat '67 standing wave.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A massive underwater sinkhole made famous by Jacques Cousteau.

A beautiful geyser under environmental threat.

England's most notorious suicide spot.

New fungal and bacterial species call this deadly lake home.

Natural time capsule containing an alien ecosystem.

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

A spectacular cave and a beguiling lake.

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

An isolated dive site teeming with cnidarians.