THis is a pretty impressive one:
"The Badwater Ultramarathon begins in the blazing depths of the Badwater basin, located in Death Valley, and goes 135 miles to the trailhead at Mount Whitney, the highest mountain in the lower 48 states. Enduring temperatures in excess of 120 F, the race starts at 280 feet below sea level and ends at almost 8,700 feet above sea level. Factoring in all the descents and ascents, runners endure over 13,000 feet of total climbing. Until 1989, the race went all the way to the top of the peak. By the time the course was changed to end at the trailhead of Mount Whitney instead of the peak, only 9 runners had completed the run from the bottom to the top.
Current course record for this test of endurance running? According to the Badwater Ultramarathon website, it's 24 hours, 36 minutes, 8 seconds, set by Scott Jurek. Even more amazing? Some runners suffer this torture-fest for close to 60 hours."