Climb right into the heart of this colorful Iceland volcano.

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

The world's oldest rose is so tough it survived being bombed in World War II.

Iceland's "Smoky Valley" is a beautiful river that is shrouded in a constant cover of steam clouds.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

These delicate sand pyramids look like naturally occurring gothic spires.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

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

An industrial site turned into Hungary's most cherished natural wonder.

The most powerful waterfall in all of Europe.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

Europe's largest natural bridge has a 19th century royal chateau built into its side.

A little-visited waterfall in an otherworldly landscape.

This army of concretions is an unexplained geological phenomenon unlike anything else in the world.

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

In Northeastern Iceland lies something of an oxymoron: a steaming desert.

400 million-year old limestone caverns nestled in the Ozarks served as shelter and a hideout for cultures throughout North American history.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

An Austrian house of bones filled with hundreds of intricately painted skulls.

This quaint Italian town keeps losing ground as the sides of its plateau slowly erode.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The glowing blue Nymphaeum of Emperor Tiberius.