I have done it before. Can't seem to find a link to the route, but it is mainly flat with one or two inclines. It goes out on a disused railway line and then back along a river bank, with the odd bit on paved road/paths. If it's rained then parts can be quite muddy and there are quite a few stiles to clamber over! I really like the half and the 9 mile race at Henfield
Edited: 29/07/2011 at 08:26