The West Highland Way is a 96 mile hiking trail between Milngavie on the outskirts of Glasgow to Fort William.
The route covers a lot of different scenery along the way as it winds its way past Loch Lomond and on to Rannoch Moor before descending to Kinlochleven and on to Fort William.
Generally the trip will take anywhere from 5 to 8 days depending on how much you want to do per day.
Camino Adventures has a useful article on the West Highland Way here.
West Highland Way
East Highland Way
The East Highland Way is a relatively new trail that goes from Fort William to Aviemore, a distance of 82 miles through broadleaf forests, loch-side trails and mountains.
The Great Glen Way is a trail that takes you from Fort William to Inverness at the northern most extremity of the Great Glen, a distance of some 79 miles.
Normally completed in 4 – 7 days it closely follows the three great lochs that mark the Great Glen – Loch Ness, Loch Oich and Loch Lochy with the first section being along the path of the Caledonian Canal.