In reply to DavidMR:
It depends what kind of disabilities you are dealing with. If its learning difficulties then the lake would be good as it could have lots of environmental stimulus.
If your dealing with moderate physical disabilities then the climbing wall will be good, although a gentle slab would probably be best. For severe physical disabilities, nice paths with lots of environmental stimulus, i.e. through the woods or around the lake, Also a viewing platform over the lake would be great. Not sure what your budget is but things like wheelchair accessible speed boats are fantastic as the participants probably wont get opportunities like that anywhere else.
Often with severe physical disabilities (e.g. cerebral palsy severely affecting all 4 limbs) the focus is more on stimulating the participants and immersing them in new environments
If you want to talk more then just email me and I'll answer. Mainly experienced with severe physical disabilities if this is what your aiming for
Hope your project gets off the ground. Probably a bit for from my disabled scout group (near glasgow) but all the best. Let us know how you get on
Cheers
David