On her 5th attempt, 64-year-old Diana Nyad successfully swims the 103 miles from Cuba to Florida in just under 53 hours. Nyad becomes the first human to do it without a shark cage. I say human, because I'm sure some other sea creatures like sharks have probably done it before.
I got to meet Penny Pelfrey a couple of years ago who has also tried a couple of times to do that swim and who completed the Cayman Brac to Grand Cayman swim of 88 miles without a cage in 2010 and it is absolutely amazing what they put themselves through to do that kind of a ultra marathon swim.