The Wall, St. Croix, U.S. Virgin Islands. The Wall is a 2-mile straight vertical drop to the ocean floor. As soon as you leave the beach, the water is shallow, warm and amazingly clear. You can swim with colourful fish and snorkel among the scattered coral formations on the ocean floor. About a quarter mile out, however, it just drops. The depth goes from 1,000 feet to 2 miles, straight down, and the water changes from warm and clear to cold and solid black. It’s like swimming over a black abyss of nothing. Just cold, dark, evil nothingness.