Mallaig is essentially a launchpad. Take the morning ferry to Armadale and a bus up Skye for a long day's exploring; aim for the last ferry back, or stay over. The Small Isles of Eigg and Rum are bigger commitments — a full day on Eigg works as a day trip, Rum really needs an overnight. The Knoydart ferry to Inverie is a half-day excursion in itself.
Fort William, at the other end of the railway line, makes a worthwhile return trip even if you arrived from that direction — the train ride is the day's entertainment, with views you cannot get any other way.
