Ecosystems

Rock-hewn monastery complex with hundreds of cave structures tucked away into the mountainside.

Bohol's unusually shaped hills turn brown in the summer months.

An abandoned Soviet-era park that, when viewed from the air, looks like a pentagram.

A cave network located at the southernmost tip of mainland Greece was once believed to be an entrance to Hades.

Final resting place of Geronimo, Quanah Parker, and the first atomic gun ever fired.

French scientists make up the majority of the few humans to occupy this remote island in the extreme southern Indian Ocean.

The hermits of Karoulia protect their asocial lifestyles by living on the vertical face of a treacherous precipice.

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

Paranormal activity on the great lakes.

Largest cave system in Africa.

Limestone caves with spectacular showcase chambers.

A wonder of natural limestone formations etched by millions of years of natural interaction between rainfall and rock and air.

Remembering the Alamo with a full-scale replica of the 1836 city.

An enormous, 30-story-deep hole in the middle of Guatemala City.

The sculptural remains of the last home of a legendary Dada artist.

An ethereal glowing blue ocean cave in Croatia.

These azure waters were thought to lead to the Mayan Underworld.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.