The XC trails at nevis range aren’t brilliant. They’re fine, like, and I like them more than most folks but they don’t really warrant a day or a big trip. Buuut, it works quite well with a train trip- nevis range is a bit of a ride from fort william but you can get onto the witches trails from the north face car park and ride in on the blue return, then at the end of the day ride out along the world champs’ xc route to get back south.
(the waymarked 10 under the ben route is absolutely shit, it’s mostly fire road. There is good riding on it but it can all be worked into a lap of the witches XC and all you miss is miles of fire road and some incredibly dull pedally singletrack.)
Much better riding down at kinlochleven, like nobeer mentioned- those “enduro trails” (walker’s paths) are fantastic, and easy to navigate too. And inexplicably, ride best in the pissing rain. Hard, mind. And not really accessible by car unless you want to do it as an overnight stay in kinloch and ride down and back. Ciaran path is massively overrated imo, it’s decent but it’s not even the best riding at kinlochleven.