5 of the World's Most Grueling Ultramarathons

Badwater, which began in 1987, is a 135-mile (217-kilometer) trek from California's Death Valley to the Mt. Whitney trailhead, at elevation 8,374 feet (13,477 meters). The course takes runners over three mountain ranges and features a searing 13,000-foot (3,962-meter) vertical ascent. And then there's the heat. The starting line in Death Valley's Badwater Basin is the lowest elevation in North America at 282 feet (86 meters) below sea level. Some of the hottest temperatures on Earth have been recorded here, and it's not unusual for runners to face temperatures around 120 degrees Fahrenheit (48.9 degrees Celsius) during the July event. To combat such intense heat, participants typically dress in white, some opting for a full-coverage outfit. Crew members keep them wet as a cooling mechanism, frequently spraying them with water, while the runners try to step only on the road's white painted markings, as the blacktop melts shoes. Although more than a few runners have developed serious medical issues during this race, due to its massive strain on the body's thermoregulation and gastrointestinal systems, it always attracts plenty of entrants for its 100 coveted spots.

There's no question the Barkley Marathons is one tough race. After all, it has a 99 percent dropout rate. Since its inception in 1986, only 17 people have managed to complete its approximate 100 miles (161 kilometers). The race is held in Tennessee's Frozen Head State Park, winding through dense forest and up and down steep mountains. But it's not difficult only because of the insane terrain, which includes 63,000 feet (19,202 meters) of elevation and lots of briars. There are no markers or aid stations on the course, which runners must navigate without phones or GPS devices. They are only allowed to study and copy a map before heading out. En route, they must find every paperback scattered around the course, then rip out the page with the number that matches the one on their bib. Participants have 60 hours to complete the race's 20-mile (32-kilometer) loop five times, which means they're running sleep-deprived and often in the dark. But one of the most difficult parts of this race is getting in. There's no race website, email or physical address. Runners have to pen an essay on why they should be allowed to compete, then find out when and where to submit it from a previous competitor. If accepted, they're sent a letter of condolence. In March 2023, for only the second time in the race’s history, three athletes completed the race.

This 155-mile (250-kilometer) trek through the Sahara Desert began in 1986 with 23 participants. Open to both runners and walkers, participants have to tote their own food and sleeping gear for seven days across unending sand, where temperatures can exceed 100 degrees Fahrenheit (37.8 degrees Celsius). Mileage varies from 13.1 to 51 miles (21 to 82 kilometers) per day, with one rest day in the middle. Participants experience blisters, sunburn and maybe even hallucinations during the daytime treks, then enjoy "peaceful" evenings sleeping in a communal tent. But they must also beware: The area is home to 12 species of snakes and 10 types of scorpions, all of which are venomous and most of which are nocturnal. If you avoid a snake or scorpion bite, you still may get socked by a sandstorm, which can diminish visibility to zero. One year, an unlucky Italian runner got so disoriented by one that he veered 100 miles (160 kilometers) off course and wasn't found for nine days. The best part of all? You get to shell out some $3,500 for the privilege of participating.

Billed as the world's coldest and toughest ultramarathon, this February event requires runners to follow portions of the trail used in Canada's Yukon Quest, a grueling sled dog race. During the 430-mile (692-kilometer) event, which has a 13-day time limit, runners can face temperatures well below 0 degrees Fahrenheit/Celsius, plus wind chills that are even lower. Fresh snow or high winds can render the marked path invisible, while river crossings can be deadly if the ice is unstable. Past participants have suffered serious frostbite and hypothermia. Runners are required to carry a sleeping bag, winter sleeping mat and bivouac bag or tent, which they pull behind them on a sled. You also need a small saw, crampons and an avalanche shovel. If this all sounds a little too extreme, you can opt to cross-country ski or mountain bike the distance instead. Or you can run in one of the event's shorter races, which top out at a mere 300, 100 and 26.2 miles (483, 161 and 42.2 kilometers).

Debuting in 2003, this 106-mile (171-kilometer) race around Mont Blanc, the highest point in the Alps, takes you through stunning scenery in France, Italy and Switzerland. But you pay for these gorgeous views via an elevation gain of 32,687 feet (9,963 meters) that batters the quads and the psyche. It also necessitates carrying a variety of clothing, as the temperatures can swing from 43 degrees Fahrenheit (6 degrees Celsius) overnight to 79 degrees Fahrenheit (26 degrees Celsius) during the day. Runners have 46 hours and 30 minutes to complete the race, and most take 32 to 46 hours to do so, spending two nights on the trail. While the race is open to 2,500 participants, it's hard to get in. Prospective runners must first accumulate 10 points by completing qualifying races within certain times over a two-year period, then hope they're selected in the subsequent lottery. The Tour du Mont Blanc is a popular hike on this same trail, and takes most people 11 days to complete.