Castle Stalker is the postcard version of the west Highlands: a compact stone tower house marooned on a tidal islet in Loch Laich, with mountains and water doing half the work. It lies well north of Oban on the road toward Appin and Glencoe, so most travellers experience it from the shore rather than as a conventional castle tour.
That is enough to make it worthwhile if you are driving the coast. The best stop is the roadside viewpoint near Portnacroish, where the castle's scale, isolation, and setting all line up. Interior access is limited and seasonal, so check ahead if you specifically want a tour rather than the classic view.