Several of my more-athletic-than-me friends have done the Tough Mudder, but that’s nothing compared to the Barkley Marathon:

Andrew Thompson is a youngish guy from New Hampshire famous for a near finish in 2005, when he was strong heading into his fifth loop but literally lost his mind when he was out there—battered from fifty hours of sleep deprivation and physical strain. He completely forgot about the race. He spent an hour squishing mud in his shoes.

From The Believer - The Immortal Horizon