The Barkley Marathons: The Race That Eats Its Young.
The people who run this definitely have a different mindset. I can't comprehend having that mindset where a simple marathon simply isn't challenging enough. Don't get me wrong - I'd love to try to make a single loop of the Barkley even welcoming the "stigma" of being runner number 1 (the human sacrifice) but I'd hate taking up one of the 40 slots for the race.
What got me thinking of the Barkley was this article in Outside Magazine on The Women of the Barkley Marathons.
Good article - good documentary - both well worth your time.