In the scorching heat of Death Valley, California, 100 ultramarathon runners from around the world converge to tackle the infamous Badwater 135. Held every July when temperatures reach more than 120°F (48°C), the Badwater 135 ultramarathon goes from the lowest point in North America to the highest point in the contiguous United States: Mount Whitney. Only 100 runners are selected every year. They have 48 hours to cross the finish line. We followed 10 of them in their journey across Death Valley.