A shed on wheels is being driven from Land's End to John O'Groats to raise money for a hospice.
It is the latest challenge for the converted Volkswagen Passat, which has been dubbed the "world's fastest shed".
It has managed a top speed of 99mph (159km/h) in tests, and owner Kevin Nicks will attempt to go faster at a track en route.
Mr Nicks, from Oxfordshire, transformed the car, which is road legal, in 2015 using steel beams and timber.
"I had a car sat there which was too good to scrap, so I came up with the idea," the 52-year-old gardener said.
"Some thought I was bonkers. One friend when she saw it, she said 'you have built your personality'."
Mr Nicks, from Great Rollright, near Chipping Norton, set off with his 14-year-old daughter Sophie earlier on Wednesday and expects to arrive in John O'Groats early next week.
One stop will be at Elvington Airfield Circuit near York where he plans to try to break the 100mph barrier.
Mr Nicks, who will be meeting supporters on his journey, said the car was always being photographed.
"It is relentless, it amazes me. It is important to me that it makes people smile... isn't it wonderful to make people smile?"
The challenge aims to raise £10,000 for Katharine House Hospice in Adderbury, which provided care for Mr Nicks's mother.