This vast, water-filled underground labyrinth can only be toured by boat.

A marvel of Byzantine engineering under the streets of Istanbul.

The most alien-looking place on Earth.

Virgil's many-mouthed gateway to the underworld.

Steaming blood-red hot spring from hell.

Sparkling, calcite-covered skeletons of children who may have been sacrificed to appease an angry god.

The ancient settlement attracts tourists from all over looking to learn about the Chinese vision of the afterlife.

This upscale streetwear store is hidden behind a fake Snapple machine in the back of a deli.

An old vending machine serves up unpredictable beverages from its seemingly magical insides.

A solitary tree has grown up all alone on Lake Wānaka, backdropped by the beautiful Southern Alps.

Where manatees are the snowbird vacationers in these balmy Florida springs.

The world's most remote permanent settlement on an active volcano.

The cafe that acts as the social hub for the small volcanic island of HMS Bounty fame.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

A stray meteor left this picturesque hole in the Australian outback.

Romania's only crater lake with water as pure as if distilled.

A lake in the middle of the tundra of Quebec is said to be the purest freshwater lake on Earth.

Mysterious craters may have been home to an ancient cult.

A dazzling temple featuring a towering 12-meter golden Buddha.

A serpentine highway twists and turns over the treacherous Norwegian Sea.

Rock-cut cave complex filled with ancient Buddhist artwork.

This complex of vertically-excavated Buddhist, Jain, and Hindu monolithic temples in India's Maharashtra providence illustrates a spirit of tolerance characteristic of ancient India.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

Stroll through a wonderland of stupendous moss-covered trees.