I agree with tricky that unless you have access to a car, most of the beautiful places are not accessible.
Though I'm from far away India, I'm in love with the Scottish Highlands and have made three visits there in four years and plan to be there again this summer.
I'd recommend travelling up the west coast from Glasgow (not worth spending time in) to Fort William, Oban, Lochinver (a small fishing village with a lot of character), Ullapool (my favourite with a lovely campsite right on the water) all the way to Durness. Balnakiel Bay has an excellent beach. Then visit the Smoo Caves and come down the centre of the country to Pitlochry where you should not miss the salmon ladder and ofcouse, Edradour - the smallest distillery in the world. Inverness can be given a miss but try and visit this town at the other end of Loch Ness (Port Arthur? - the name escapes me) which has an interesting series of lockgates.