Okay maybe floating face down in a swimming pool isn't for everyone. How about free-diving? The problem with this is that there are all sorts of categories including 'no limits' where divers use a weighted sled to pull them down and then air bags to ascend. You still have to hold your breath of course... The world record for this is an amazing 214m (over 700 feet). But the purest form of the sport is where the diver swims down and back under his own power without even the benefit of fins. Watch this amazing dive by William Trubridge, who has set further records since this video. I love how calm and collected he is. Every movement seems perfectly choreographed and he is clearly maximizing efficiency and not speed.