I’d second (third/fourth or whatever we’ve got to) the Western Isles and back via Skye and Mallaig “loop”.
We got the train to Oban, ferry out to Barra, B&B near the Eriskay ferry. Up the Uists and Benbecula to another B&B. Ferry over to Harris, up to Tarbert and ferry over to Skye, B&B in Portree. Down to Armadale, avoided most of the frankly awful main road on Skye by taking the west coast of the island down to Sligachan, hostel in Mallaig. Down to Kichoan and ferry over to Tobermory, stopped in the YHA there. Looped round the island to get to Craignure, stopped in the pub. Ferry back to Oban, train home.
The hardest day was going up the Uists as there was a strong northerly blowing and it was just hard work. The other days were just standard touring fair of: ride for a couple of hours find a café, ride a bit more, find another café, ride to destination (maybe with another café).