http://www.youtube.com/watch?v=S06oMxdt40A
As far as I know, it gets even more extreme. For their qualifying test to become monks, they must run ultra marathons 1000 times, over the course of 7 years, ending with over 50 miles a day for months on end. If they fail, they must kill themselves. Only 46 have ever passed the challenge.
And for anyone who is about to post a comment criticizing these monks, don't. I don't seriously believe that they are the greatest athletes on the planet (though they could be).