Virgin cave systems comprise some of the last unexplored regions on our planet. Late last year, for the first time ever, a group of cavers photographed a cave in China that's so vast it even has its own weather system.
But for those who deem caving - or spelunking - a little too adventurous, camera-wielding cavers have captured the beauty of the earth's interior.
Here are 12 of the most breathtaking caves in the world.