Comedienne Jo Brand is following in the footsteps of David Walliams and Eddie Izzard by attempting a gruelling challenge for Sport Relief.
The 58-year-old will brave sore feet and blisters as she sets off on a 150-mile coast-to-coast trek which she aims to complete in seven days.
The challenge, called Jo Brand's Hell of a Walk, starts in Hull on Friday and is set to finish in Liverpool on Thursday January 28.
Brand said: "When I first started training for this challenge, I didn't realise I was not the national fitness icon I'd always believed myself to be. My body is a temple - it's big and it doesn't move!
"The realisation is gradually dawning that I have to walk a very, very, very long way, with many days back-to- back using only my poor little legs to carry me, and that's a gruesome thought.
"But the hope is that the walk will raise much-needed funds for people who really deserve it, which will keep me going. And, if it doesn't, I will give Greg (my trainer) full permission to push me off the top of a massive hill."
With temperatures plummeting across the UK, Brand faces the prospect of snow and ice when she climbs up to 1,530ft while crossing the Pennines. She is expected to take 60,000 steps and burn around 6,000 calories each day during the challenge.
The former psychiatric nurse hopes to highlight the work done by Sport Relief around mental health issues in the UK and across the world's poorest communities.
Brand's challenge, which is being sponsored by BT, is the latest in a string of endurance tests carried out by celebrities for the charity.
David Walliams raised more than £1 million after swimming the length of the River Thames in 2011, while Eddie Izzard ran 43 marathons in 51 days in 2009. John Bishop and Davina McCall have also completed challenges for Sport Relief in recent years.
Brand's walk will be filmed for a BBC documentary to be broadcast in the run-up to the Sport Relief weekend, which is taking place from Friday March 18 to Sunday March 20.
Anyone wishing to sponsor her can visit www.sportrelief.com/sponsorjo.