The Barkley Marathons is a mysterious ultramarathon held every year in a state park in Eastern Tennessee.
Runners have to complete five loops of a 20-mile course that most say is really 26 miles, making the race somewhere between 100 and 130 miles in total.
The elevation and descent in the race mean that finishers do the equivalent of climbing and descending Everest twice.
Since 1989, only 15 people have finished the race.
For a runner who tries to enter the Barkley Marathons, one thing is...