I work at Ticket to Ride bike hire in Inverness and deal with this query on a daily basis 🙂
GGW to Abriachan, play around on the trails, visit the most unique eco-cafe and back is a decent day for most folk. There are more serious DH trails around the mast above Craig Phadraig too.
The A82 is best avoided. Not that there are lots of accidents but it’s really unpleasant for cycling.
South side of Loch Ness has lots of quiet roads yoy can link up. Dave Barter features one route in his “Best British Cycling” book. Good cafe at Foyers and publish at Dores.
The Black Isle and Beauly Firth are other good road routes but we can provide GPX files given some notice and a decent outline of requirements.