These sub-farmland caves are home to a majestic stalactite known as the "Crystal King."

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

The only Florida state park with publicly accessible caves.

This massive underground salt mine now holds a sci-fi theme park in its depths.

This massive subterranean fissure is known as the "underground Grand Canyon."

The wartime boat shelter now doubles as an underground concert hall where musicians play on rafts along the waterway.

The true depths of these stunning Moroccan caves are unknown.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

These layered sandstone mountains in China look like they are made of pressed crayons.

This vertical pinnacle in China was the inspiration for the floating mountains in the movie “Avatar.”

A sinkhole and now a swimming hole, too, full of dazzling turquoise water.

Romania's "Red Ravine" is a little-known natural wonder that bears a resemblance to the Grand Canyon.

Climb down into the largest sinkhole in Qatar.

Raging waters have created a strange geological site that looks like something off of a progressive rock album cover.

After millennia of erosion by sand and churning water this Brazilian valley now looks like a lunar fantasy.

A massive natural rock arch gives the Tuscan mountain its own window to the sky.

A long, winding trek rewards you with a gorge so captivating it inspired a painting in the Tate.

The land is full of geologic eye candy, such as otherworldly spires, mushroom-shaped hoodoos, and prehistoric fossils.

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

A star-shaped fortress town fort built in the geometric model of the Renaissance utopian city.

A lush indoor jungle fills this bustling Madrid transportation hub.

This unusually shaped mountaintop tower looks like a UFO floating over the city.

In medieval times this small stone seat was used as a bizarre way to punish insolvent debtors.

This dizzying span over the ancient Algerian city was once the highest suspension bridge in the world.