Legendary explorer Ranulph Fiennes is competing to become the world's oldest Briton to finish the 'toughest footrace on earth'

Sir Ranulph Fiennes, touted as the "world's greatest living explorer," is in the final days of training for his latest challenge: a six-day, 156-mile race across the Sahara desert.

If the 71-year-old completes the Marathon des Sables - dubbed the "toughest footrace on earth" - he will become the oldest Briton to do so, according to the Guardian.

The Marathon des Sables, which starts this Sunday, is the same as running 5 1/2 marathons. Although participants are given a tent to sleep in at night, they must carry their own food and other equipment. The race will take competitors "across saltpans, up desert-mountains, through ruined towns and through the occasional sand storm," according to the marathon's official website.

Fiennes lives for these types of adventures. He has earned his reputation by surviving the most hostile environments on earth. This includes being the first person to visit both the North and South Poles, and scaling Mt. Everest. He's become well-known for sawing off his own frostbitten finger tips on a journey across the Arctic. The British adventurer's last record-breaking expedition took him all the way to Antarctica, where he and five other explorers attempted to be the first to cross the icy continent in the winter.

That mission came to an abrupt end when Fiennes was forced to pull out of the expedition early due to severe frostbite.

But the daredevil is now back in the game. He has been training with veteran marathoner Rory Coleman, the Guardian writes.

"The thing that sets Ranulph apart is that he's not trying to buy the medal," Coleman, who will be running with Fiennes, told the Guardian. "I think a lot of people are trying to buy a life experience. They're trying to be a James Bond for a week. Whereas Ranulph … he IS James Bond. He's the real life 007. When I've been with him people come up and it's almost like they want to touch his cloak and feel the power. He's a proper national institution."

Fiennes has been prepping for the grueling race in his native England. "Last week my wife dropped me off at the top of the Sandstone Way and picked me up at Whitchurch," he told the website. "I timed it and it worked out as 3.4 miles an hour for about 32 miles. The trouble was I didn't have a heavy weight on my back: 7kg doesn't sound very much, but it starts feeling heavier and heavier."