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

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

This centuries-old Italian chapel hangs midway down a sheer cliffside.

A fiery crater has been burning in the Karakum Desert since 1971.

A massive Celtic cross secretly growing in an Irish forest.

"Where the ducks walk on fish."

Humboldt's human-powered sculptures race across land and sea for days on end in a wacky quest for dominance.

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

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

The house that took a plunge into the facade of a museum.

A seemingly endless landscape of pure salt stretches far across Bolivia.

Abandoned railway line circling the city of Paris.

Mysterious chains and iron stakes adorn this strange grave, with no explanation.

The centuries-old trees lining both sides of this dirt road may become Madagascar's first natural monument.

Considered the birthplace of the Copper Age and Bronze Age, the river is tinted red from 5,000 years of mining.

Now famous as the "Harry Potter bridge," this impressive concrete viaduct has long been an icon in its own right.

A brightly colored natural bridge formed by mineral-rich hot springs high up in the Andes.

Roughly 17 million letters to Santa have found their way to this Arctic Circle post office.

An underground city of salt.

This bizarre English competition answers the important question: how many worms can YOU coax out of the ground?

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

A miniature train-ride through Slovenia's largest cave system.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.