In reply to zarathustra:
I think a lot will depend on other factors. Is the chair user relying on someone to push or is s/he self propelled?
I'm able to push my 19 year old daughter along forest tracks, disused railway lines (as already mentioned above) and often on some steep gradients. But not everyone has the ability to do this.
Also, where accessible tracks have been provided they tend to be very short. I saw one yesterday at Dol Idris (Cader Idris area in north Wales), but it claimed to be a 30 minute walk. In my experience that would more likely be about half that. I didn’t explore it, but might go there with my daughter at some point.
The problem with mountains or hills is often the width of the path or track, or with cambers on tracks that contour around a hill (wheelchairs tend to tip over).
Sorry - all my points are a bit obvious and not at all helpful, but I will be interested to see what suggestions you receive here.
Post edited at 14:14