Guillaume Nery is base jumping at Dean's Blue Hole, the world's deepest known blue hole with seawater. It's a 663 foot plunge into VERY DARK water west of Clarencetown on Long Island, Bahamas. Guillaume's girlfriend filmed his base jump that is said to have been filmed on 1 breathe.  

 

Here's a piece 60 Minutes did on this exact place...very interesting AND SPOOKY! Seems it pulls you down, which answered one of my questions when I watched Guillaume's video above, "how did he keep going down at such a fast rate and not really swimming hard?"