from: This Is Somerset
As they stretch their muscles to the limit climbing mountain passes and undertaking a 1,400-metre dirt road descent to the rainforest below, their thoughts will be focused, not on the beauty around them, but on a Somerset cottage and a child who has already defied medical experts.
Olivia Yorke-Dunne, who will be four in October, has been fighting vicious neuroblastoma for half her young life.
It is one of the worst cancers a child can get, with a very low survival rate in high-risk cases.
Olivia, who lives with her family at Norton-Sub-Hamdon, near Yeovil, was diagnosed with the condition at Bristol Children's Hospital, not long after her second birthday. 
As she has battled her illness, enduring chemotherapy, surgery, and specialist radiotherapy in London in which she received a radioactive isotope into her bloodstream, the West-based charity CLIC Sargent was constantly at hand to offer Olivia and her family vital practical and emotional support.
Her father, Tim, mother, Karen, and brother and sister, Mollie, nearly three and Thomas, nine months, have spent many months staying in CLIC accommodation in Bristol to be with Olivia as she underwent treatment. Her godfather, Iain Balchin was determined to raise money for CLIC's continuing work for child cancer patients and their families, and singed up for the charity's Andes to Amazon cycle ride which takes place next month.
He now lives in Shropshire but used to live in Wiltshire, and soon four friends of his from Wiltshire – John Keppel, Anthony Higgins, Christopher Spratling and Ben Leighton had signed up. Between them they hope to raise £25,000.
A bone marrow transplant last year did not have any effect on the cancer, and now, although only 0.5 per cent of the cancer remains in Olivia's bone marrow doctors consider her condition incurable.
Mr Yorke-Dunne said: "She is having chemotherapy but we were told in January that if we wanted to do any special things we should do them in the next three months."
But Olivia continues to defy the consultants.
Olivia is back at home now and a CLIC Sargent nurse visits her and the family twice a week to take blood samples.
She is also still receiving chemotherapy treatment.
Mr and Mrs Yorke-Dunne said: "We are so grateful for the wonderful help we have had from CLIC Sargent.
"Our family would not have been able to stay together without them."