Runners love a challenge. Ultra-Marathoners crave them, and there are several races where even the most experienced long-distance runners have met their match. These marathons are created to bring the world’s best runners together to face some of the most daring and risky foot races. These are not your ordinary ultra-marathons. These courses are known to weed out the everyday marathoner and show who is the ultimate long-distance runner. Ranging from scorching deserts to frigid mountain ranges, the following races have been known to injure a few unlucky participants; some have even lost their lives while competing. Despite many breathtaking views and spectacular scenery, these ultra-marathons also reveal to some runners’ their breaking points. Here is a list of ultra-marathons that most long-distance runners consider as the most challenging courses in the world, either for their toughness, distance, or climate.