The Plain Endurance Runs are a legendary test of self-sufficiency and grit in Washington’s Cascade Mountains. With no course markings, no aid stations, and no pacers allowed, these races demand that runners rely entirely on their own planning, navigation, and resilience. Known as one of the toughest ultras in the country, the 100-miler has seen years with zero finishers. For those seeking the full experience on a slightly smaller scale, the 100K offers a single-loop challenge through remote and rugged terrain.