Though it is called Stargate, this alien landscape is found on Earth. One of the submerged caves, or blue holes, of the Bahamas, it is extremely difficult to explore but a treasure trove for scientists. Photo by Wes C. Skiles for National Geographic
Cave diving,only those who are properly trained and properly equipped should ever enter a cave system underwater. If you are an Open Water Diver, equipped for that sport, you have no business in a cave.