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.
A pair of divers explore the wreck of the Giannis D (originally Shoyo Maru) on the Abu Nuhas reef, Strait of Gubal, Red Sea, Egypt. By British photographer Alex Mustard. He's travelled the world snapping pictures of wrecked ships lying on the sea bed.