Imagine this: five days, 320 kilometres, 8 ½ miles of ascent through the mountains. Could you do it? If you said yes, then what are you doing reading this?
You should be in Wales for an event called the Dragon's Back Race - quite possibly the toughest race in the world. This week, nearly 100 competitors started the race and now they're in the fifth and final stage.
Now, if you've never heard of it, that's understandable. The Dragon's Back Race has only been run once before, 20 years ago in 1992. But now, it's back.
The race started on Monday on the north coast of Wales and ends today. The competitors have to run 320k along the mountains of Wales, from the top to the bottom (about 45,000 feet in all) on incredibly rugged terrain - steep, rocky, slippery, foggy, cold you name it.
If that's not enough, there's no defined route, no trails, nothing except a few checkpoints noted on a map released the morning of each stage. Apparently, even the best endurance athletes have trouble figuring out the best way to go. And as they run, the pay a price - pain, cuts, bruises, some get disoriented, and each day it gets tougher.
In 1992, 55 runners took part in the race. Only half of them made it to the last day. In fact, one of the top endurance athletes in the world - Sweden's Rune Larsson - got trapped at one point on a rockface and didn't know how to get off.
As he told the British paper The Independent "I was lost in the mist in a strange country and felt very alone... frightened and thinking of my seven-month-old son."
300 people applied to enter this year's race. Organizers selected just over 90 runners from around the world - the U.S., the U.K., Canada, France, Germany, Spain, Scandanavia, Australia, New Zealand, South Africa and Belgium. They run in pairs, just to keep everyone safe. And they stay in campsites at night, with food provided by catering companies.
One of the competitors this year is Helene Diamantides. She's 48, a physiotherapist and mother of two small girls. She's also a record-breaking mountain runner, who was part of the winning pair in the original Dragon's Back Race 20 years ago - when male ultra-runners didn't think much of a woman in their race.
You can read more about Diamantides, the race, and the guy who organizes it in this piece by The Independent.
Plus, The Guardian has put together an incredible collection of photos from the Dragon's Back Race. Check them out here.
And here's a few other ultra-marathons and endurance events to test your metal.
Yukon Arctic Ultra - known as the world's coldest ultra, the toughest level involves nearly 700 kilometres on snow from Whitehorse to Dawson City. You can run, cycle or ski it but be warned, temperatures can drop to -50 degrees celcius.
Badwater Ultramarathon - this one is in Death Valley, California. It starts at 85 metres below sea level and ends 215k later, 2,530m above sea level, at Mount Whitney, Temperatures can get as hot as 55 degrees celcius.
Norsemen Extreme Triathalon - if you enter this one, be prepared to be dropped off the back of a ferry nearly 4km offshore, then swim to shore, hop on a bike and ride 180km, then jump off and run 42 km - uphill.
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