This is the Subwing, and it promises to give you the feeling of flying underwater. The concept is pretty simple: Hold onto a large wing, get towed behind a boat and hold your breath for as long as you can. It's terrifying and awesome at the same time, which is the sign of any good sport, really.
The German-designed Subwing is made out of fiberglass or carbon so it's lightweight, and the tow line itself is similar to one used for water skiing or wake boarding -- which means there's full motion underwater. It looks pretty awesome.