British adventurer Sir Ranulph Fiennes is attempting the 'toughest footrace in the world', the Marathon des Sables.
It involves travelling more than 150 miles across the Sahara desert, in north Africa, in just six days - the equivalent of doing a marathon every day.
In doing so he'll have to battle temperatures of up to 50C.
If he succeeds he'll be the oldest Brit ever to complete the event.
It's not the first extraordinary adventure Sir Ranulph has attempted having climbed Everest and trekked across Antartica as well as once running seven marathons, in seven days, on seven different continents.
Watch Jenny's report to find out more.