17 of the most alien-looking places on Earth

Socotra Island, off of Yemen, is home to the weird-looking Dragon's Blood Tree. In fact, a third of its plant life isn't found anywhere else on the planet.

Expansive fields of sulfuric ponds make the Danakil Depression in Ethiopia one of the most inhospitable places for human life on the planet.

The ominous Tianzi Mountains in China actually inspired Pandora's floating mountains in "Avatar."

Ireland's Giant's Causeway consists of 40,000 super symmetrical volcanic rock columns — the extraterrestrial-looking result of an ancient volcanic eruption.

Deadvlei in Namibia is an eerie, bone-dry expanse littered with dead, skeleton-like, Acacia Trees.

China's brightly colored Zhangye Danxia mountains were formed by 27 million years of red sandstone erosion.

The Richat Structure in Mauritania, also known as "The Eye of the Sahara," is a 25-mile-wide dome that is thought to be the result of erosion... not an alien crash landing.

New Zealand's ancient Waitomo Glowworm Caves are brightly lit thanks to ceilings covered in thousands of tiny glowworms.

Red Beach in China is a sprawling wetland that gets its distinct hue from Sueda seaweed, which turns a vivid shade of crimson in the fall.

Aptly named, the Door to Hell in Turkmenistan is a gaping, 226-foot-wide hole that was created in 1971, when a Soviet drilling rig collapsed into a natural gas cavern. It's been burning ever since.

The Devils Tower in Wyoming is a 1,267-foot-tall rock formation that was fittingly the site of alien thriller "Close Encounters of the Third Kind."

The bright red Wadi Rum desert in Jordan often doubles as Mars in movies, like in the recent blockbuster film "The Martian."

The eerie, azure-colored Marble Caves in Chile are carved into a peninsula of solid marble in a glacial lake that spans the Chile-Argentina border. They are the result of 6,000 years of wave erosion.

For more photos of the Marble Caves, click here »

Salar de Uyuni in Bolivia is, at 4,000 square miles, world's largest salt flat. When it rains, its surface essentially turns into a giant mirror.

The Cave of the Crystals in Mexico is 980 feet below-ground, and features some of the largest natural crystals ever found. Temperatures in the cave can reach a balmy 136 °F.

Arizona's Antelope Canyon is a surreal sandstone canyon formed by flash floods and monsoons over the course of millions of years.

Chocolate Hills in the Philippines are grass-covered limestone mounds that turn brown during the dry season. Hence the name, Chocolate Hills.