In reply to BigLob:
As above, narrow it down a bit, its a huge area!
There's a nice track from Gruinard in to Loch na Sealga which gets you into some wild country.
From Craig in Glen Carron you can get up an easy, but with one longish climb, track towards Glenuaig Lodge.
From Poolewe you can get up to Fionn Loch on a Landrover track, there is climbing.
All those are "there and backs" used to access quite remote areas. Circuits are a little harder unless you start contemplating singletrack or "hike a bike" sections.