Every year in the backwoods and mountains of Tennessee, 40 ultra-runners and extreme fitness enthusiasts attempt to complete the most gruelling, bizarre, and secretive race of the calendar year. The brainchild of an eccentric former runner — memorably going by the moniker Lazarus Lake — The Barkley Marathons promise 100 miles of punishing, unforgiving terrain across five laps, unpredictable springtime weather conditions, a 60 hour time limit, and runners can only use a master map they have charted themselves as a guide. Founded in 1985, no one was even able to complete the race for a full decade, and only 10 have completed in the ensuing years. The eccentricities don’t stop with the physical side of things. Participants must first pass an entry exam, pay a non-refundable $1.60 entry fee, produce a license plate from their home state or country if it’s their first time racing, and bring Lazarus a flannel shirt.

Filmmakers Timothy Kane and Annika Iltis have a similar handicap to that of the runners: there’s a lot of ground to cover. Kane and Iltis bring a remarkable attention to detail and organization befitting of their offbeat subject. The Barkley Marathons has a unique degree of unpredictability, as it bounces around between the history of the race and the lives of a new batch of participants, but it does this with a structure that never feels scattershot. As the race progresses, tension genuinely builds, and the film takes on a hard earned inspirational tone as the field of largely amateur athletes gets whittled down drastically. Audiences will be laughing and scratching their heads throughout (and none will probably ever want to attempt such insanity), but by the end they’ll be cheering.