It's the remains of an old military road (built after 1715 Jacobite rebellion). Was used by the Scottish SIx Day Trial (motorcycles) because it was "interesting" on a motorbike, but vehicles are now banned.
You could ride it (carefully) on just about any bike apart from a few short sections. A mountainbike makes it relatively straightforward. It's worthwhile because of the great sweep of landscape, the sense of isolation, and a good day out.
The weather can be completely different on one side to the other.
Good dry weather, it's simply a great ride. Highland special for heroes weather, and you have a major challenge part of which may consist of trying to stay alive. People have died up there – don't know if it has claimed any cyclists though.
If you can ride up the zigzags you're better than average.
The large round rocky boulders section is tricky too – I walk that bit because I don't fancy the risk of injury if I'm on my own.
I hope to be riding it again in the next 2 weeks, so I'll stick some pics up if I do.