A cave is "a natural opening in the ground extending beyond the zone of light and large enough to permit the entry of man," according to the U.S. Geological Survey. Caves can range in size from single rooms to large formations with winding passageways that extend for miles. Caves typically form in types of rock, such as limestone, that dissolve in water. It can take tens of thousands to hundreds of thousands of years for caves to form. The study of caves is called speleology, and the exploration of caves is called spelunking. Caves are famous of their dripstone features called speleothems, the most well-known of which are stalactites and stalagmites. Many of the strange creatures found in caves have adapted to live in near or total darkness — some are blind to visible light. See cave pictures and read about the latest cave discoveries and speleological research below.
A group of ring-tailed lemurs in Madagascar have made caves their nightly sleeping spot and are the first wild primates ever observed to return to the same caves night after night to rest.
A new attraction in central Kansas allows tourists to travel 650 feet (198 meters) underground and explore an active salt mine, and revel in the shimmering crystals.
More than 3,000 feet below ground, a new snail species has been discovered with a delicate, translucent shell.
Now-extinct carnivores, such as saber-toothed cats, were lured to enter a deadly underground cave by the smell of rotting carcasses
From crystal caves to never-ending lightning storms, here are some of the wildest and most unique spots on the planet.
Modern polar bears all seem to share some genes. It just so happens these genes come from an Irish brown bear living over 20,000 years ago.