The Ben Nevis leg is like this:

You dock at Corpach lock, run along the "coast path" by Caol (Great Glen Way) in a SE direction. You cross the river on a footbridge by the Mallaig railway line bridge (I think it is the same bridge, but may be wrong there). Run through Inverlochy, then up the north / east bank of the Nevis river along the minor road. Pass Achintee House, then up the main Ben Nevis path. You're not meant to take the Red Burn path shortcut (I think that's what it's called), but can cut the zig zags after that (according to choice). The checkpoint is on top of that big cylindrical cairn on top. The way back is the same as the way up. The finish line is by the lock in Corpach.

There is only one checkpoint on this leg: at the top.

[Note: the 2008 route is described above. The 2007 route started off / finished along the A830].