St Christopher's Hospice organises a Fun Walk every two years. I have taken part in all but one of the walks since my Mother's stay in St Christopher's in 1991. I usually do the longest of the routes around Keston and, by the end, I can assure you that it isn't as much fun as it was at the beginning. I think it is 11 miles this year!
More information about the walk and the hospice itself can be found at the St Christopher's Hospice
Alternatively, I would be more than happy to receive sponsors on-line via JustGiving.com: http://www.justgiving.com/StChhersRobWilliams