It's one of the world's hardest races to get into, with spots filling up just minutes after they become available.

The race is called Survival of the Shawangunks, or SOS for short. Why are serious athletes flocking to the Hudson Valley every September for this event? Well, maybe because it's one of the most difficult endurance races in the world.

Slowtwitch reports that the SOS began back in 1983. The race takes advantage of the natural terrain, setting it apart from many other triathlons and Ironman-type races. Participants begin by biking 30 miles. After that, a 4.4 mile run leads to a 1.1 mile swim through Lake Awosting. After that, it's another 5.5 mile run over Castle Rock, which reaches an elevation of 2400 feet. Another half mile swim through Lake Minnewaska lead to an 8 mile run through the trails. While that would be more than enough physical activity for even the most well-trained athlete, it doesn't end there. After the eight-mile run, participants jump back in the water for a final half mile swim before sprinting .7 miles to the finish line.

If you're like most people, you're probably exhausted by just reading about all of that running, swimming and biking. But serious athletes are so desperate to participate in the SOS, that the website generally fills up all 150 spots just minutes after they become available.

This year's race took place on Sunday, September 9. Timothy Clarke from Astoria finished first in the men's category with a time of 4:38:15. The fastest woman was Jamie Turner from Memphis who finished at 5:21:27.

If you're interested in entering next year's race, you can find out more information about the Survival of the Shawangunks on their official website.