The Barkley Marathons consists of five loops, 20 miles each, along unmarked trails in rural Tennessee, with about 67,000 feet of elevation.
CNN
Runners must trace the course from a topographical map hours before the race begins. Four or five pages of enigmatic and wry instructions are also handed out.
David Allan/CNN
If accepted into the race, runners get a "letter of condolence." They're told the date of the race and must bring a license plate of some variety to the race site.
David Allan/CNN
A conch is blown one hour before the race starts, but that can be anywhere between midnight and noon. The race's creator, known to everyone there as Laz, reads the names of former racers who died, and a bugler plays taps, the traditional song of military funerals.
David Allan/CNN
No GPS or phones are allowed on the race. The only permitted technology is a cheap watch from Walmart, handed out by Laz to each runner and synchronized to his watch. The cutoff time is 60 hours.
CNN
Though most other distance races -- with their clear routes, aid stations, teams of helpful volunteers and throngs of encouraging spectators -- are designed so racers finish, the Barkley is designed so racers fail.
David Allan/CNN
Barkley runners jump into a creek and wade through a tunnel that goes under Brushy Mountain State Penitentiary. It was the prison escape of James Earl Ray -- who assassinated Martin Luther King Jr. -- that helped inspire the race.
David Allan/CNN
The race checkpoints are unmanned and in the form of paperback books. You rip out the page that corresponds to your bib number to prove you reached it. The books often have tongue-in-cheek titles.
CNN
Of more than a 1,000 who've entered, only 17 have completed the full distance in time in the race's history.
