I have seen a fair amount of Scotland by public transport so wanted to share the August itinerary that I did across the country to it can demonstrate that a lot of the country can be seen primarily using trains and buses to move around. The drawback is that the schedules are fairly rigid and need to be planned out due to few connections a day in the Highlands and Islands.
Day 1: Glasgow to Oban by ScotRail train - Saw the distillery
Day 2: 3 Isles tour of Staffa, Iona and Mull by West Coast tours departing Oban - only 3 hours on the ground sightseeing but well worth it if pressed for time. Ideally, spend a weekend on Mull.
Day 3: Scottish Citylink bus 918 to Ballachulish from Oban in the morning - Dump bags and take afternoon bus to Glencoe 3 sisters, return by the evening bus.
Day 4: Bus 916 to Portree from Ballachulish in the morning - See the town on Portree
Day 5: Skye day trip with Skye Scenic tours - Local guide that I highly recommend having used them 3 times myself.
Day 6: Morning bus from Portree to Eilean Donan castle (pictured) - See the castle till noon, get the afternoon bus / taxi back to Kyle and the afternoon train to Inverness.
Day 7: Catch the local bus 19/119 to Loch Ness Clansman hotel from Inverness - Do the Jacobite boat tour. Return in the afternoon and catch the train to Carrbridge. See the 300 year old bridge. Catch the evening train to Aviemore for dinner and the night train back to Inverness.
Day 8: ScotRail train from Inverness to Edinburgh - End of trip.
Hope this helps, I have done 3 flavours of this circular trip by public transport. I also recently documented specific public transport details for a small set of famous castles I saw by the same method. See list of such castles here, hope the help non-drivers like myself.
