Barkley marathons is known for its navigation challenges and is considered one of the hardest and most eccentric races worldwide. (Image: News18 Creative)

The world’s oldest 100-mile race, Western States presents elite competition and scorching heat. Runners face the brutal central California summer temperatures, including a grueling stretch called the Canyons, with unforgiving climbs and descents. (Image: News18 Creative)

Revered for its steepness and remote terrain, Hardrock covers 100.5 miles in Colorado’s San Juan Mountains. With a cumulative climb and descent of 30,000 feet, including elevations above 14,000 feet, securing a spot through the lottery is a challenge in itself. (Image: News18 Creative)

Ultra-Trail DU Mont-Blanc (UTMB) is a prestigious 100-mile ultra-race that transverses France, Italy and Switzerland around Mont Blanc. (Image: News18 Creative)

A seven-day multistage race in the Sahara Desert, Marathon des Sables covers roughly 150 miles. Participants endure extreme heat, sandy dunes, and self-sufficiency, carrying their own supplies. (Image: News18 Creative)

The Rut is a Montana 50K race known for its exposure, technicality, and significant elevation change. With over 20,000 feet of elevation gain in 31 miles, runners tackle highly technical and exposed terrain that demands physical and mental strength. (Image: News18 Creative)

Known for its extreme heat and distance, Badwater 135 takes runners through Death Valley, where temperatures exceed 110 degrees. (Image: News18 Creative)

Although it’s the shortest race on the list at 3.1 to 3.5 miles, the Mount Marathon Race in Alaska is intense. With over 3,000 feet of elevation gain, including scaling an exposed cliff, it is a technical and dangerous race that draws huge crowds on the Fourth of July. (Image: News18 Creative)