IT makes the London Marathon look like a stroll in the park!
Instead of 26 miles in pleasant spring weather, how about 150 miles in searing heat?
And when the water is rationed and the challenge is across one of the world's most inhospitable regions it's hard to see why anyone would want to do it.
But Peter Birkett, of Bradley, was a man to accept the challenge of the Sahara Marathon.
He spent months in training and completed the equivalent of five-and- a-half marathons in an amazing 33½ hours.
Others were not so lucky.
Peter was one of 760 competitors in what is billed the world's toughest footrace - and 185 dropped out in the first three days.
"It was not surprising," said Peter, 43, now recovering back at home.
"The temperatures reached almost 50 ºC (120° F) and they were rationing the water we were allowed to carry.
"Sensibly, as the temperatures continued to get hot, they revised their rationing and we could take on more water.
"But an Irish runner collapsed into a coma and another suffered a stroke in the heat.
"But I'm proud to say I was able to keep going. I've done it."
Peter, a director of a management services company, lives with wife Judith and children John, 14, Jane, 12, and Peter, 11.
He is a man with several marathons behind him and has also competed in triathlons and an Ironman competition, running, cycling and swimming long distances.
"You can't really create the Sahara conditions in a Huddersfield winter," said Peter.
"But I worked hard at the training, running up to 12 hours a week to try and build up my strength.
"I am a naturally fit guy but it was hard - especially as we had fierce sandstorms for the first three days and the heat was unbelievable.
"All the runners have to carry their own food, clothing, maps and tents, so there is a lot of weight on your back as you run.
"But it was a challenge and I'm glad I have done it.
"You need to be fit and should not be able to see `walk' as a swear word. Even the top competitors were reduced to walking some stretches.
"My two boys are now chattering on, saying they'd love to do it.
"I just want to put my feet up, but I know there will be other challenges.
"I fancy having a go at golf next!"
But Peter's efforts - which secured him 20 blisters on his feet - paid off for charity.
He has raised £15,000, which will shared between the NSPCC and the Yorkshire Air Ambulance.