Good friends Graham Cox and Laurence Duffell, known as the Cox and the Fox, are completing the 80-mile challenge as a tribute to Graham’s late wife, Carol, who died in March.
Carol, who was 53, had breast cancer and latterly a brain tumour.
The walk will raise money for the West Sussex Breast Clinic, based at Worthing Hospital, and Macmillan Cancer Support.
Laurence, 57, said: “We started planning the walk before Carol died, as she thought the clinic and the staff there were just amazing and so understanding of what she was going through.
“Then, in March, her condition worsened quite quickly, and she died very suddenly.
“It was then that we really had the extra impetus to take the plans for the walk further.”
The pair started their walk today (Sunday, September 18), following the route of the towpath along the Kennet and Avon Canal between Bath and Reading.
They hope to finish on Thursday.
It will be extra challenging for Graham, 58, of Cleveland Road, Worthing, as he is registered blind.
Laurence, from Yapton, added: “We hope to raise around £5,000, although I think the final tally may be closer to £3,000.
“The clinic is just such a wonderful place, and Graham still pops in there now to chat to the nurses when he’s collecting sponsorship forms.
“It’s just nice to know that they have been through these situations before.
“They just know the right things to say and they are so kind, and I know Carol found it extremely comforting going there. We want to do whatever we can to help them.”
To sponsor Graham and Laurence, visit www.justgiving.com/Walk-for-Carol-2011