Inside, rough stone walls line passageways and rooms, reminding visitors that they are just as much in a castle as they are in the body of, essentially, a huge rock.

The scalloped rock walls suggest fast moving waters in this passage deep underground in Clearwater Cave, Sarawak, Malaysian Borneo. Clearwater Cave is the 8th longest in the world. Photograph by ...

The caves weren’t five-star accommodations with internal hydroelectric power plants and brick-lined walls–the kind sometimes imagined in the computer-generated images of the press.

That’s when a 200-foot passage was dug through the back of the cave and a parallel tunnel was blasted through adjacent rock. You can still see the original “cave” part of the tunnel in the rough rock ...

Well, if you've clicked on this story, you already know a little bit of what you're in for. But the cave house of Glenwood Springs is more than meets the eye, and we'll take you inside to show you ...

The Marble Caves sit on the shores of a turquoise glacial lake in southern Chile. Light bounces off the water onto the walls, creating a magical, ever-changing display inside the caverns.

More than 57,000 years ago, a human traced their fingertips along the chalky wall of a French cave, leaving shallow, parallel furrows behind. But what species were they?

The Marble Caves sit on the shores of a turquoise glacial lake in southern Chile. Light bounces off the water onto the walls, creating a magical, ever-changing display inside the caverns.