Stalactites and stalagmites in a beautifully lit cave.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

In Portugal, a secluded stretch of untouched natural beauty hides at the bottom of a steep hill.

A perfectly circular lake is formed by the crater of an ancient underwater volcano.

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

A unique seaside cave where Aleister Crowley faked his own death.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

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

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

Rising from the sea like a stone monster.

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

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

This fantastical waterfall is hidden in a cave located in a cracked cliff.

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

Climb right into the heart of this colorful Iceland volcano.

The most powerful waterfall in all of Europe.

Strange rock formations tower above the river that snakes through this enchanting Icelandic canyon.

This elegant arc of a waterfall marks a religious turning point.

A winding, blood-red tunnel of hardened lava navigable by foot.

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

These ominous lava formations were said to be an entrance to the netherworld so of course they inspired a famous metal band.

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

Three columns of volcanic rock shoot out of the ocean.

The largest whale museum in Europe allows visitors to walk among life-size giants.