Carnasserie Castle is a roofless but impressive 16th-century tower house north of Lochgilphead, close to Kilmartin Glen. Its ruined walls still show the ambition of a fortified residence built for status as much as defence, with stairways, chambers, and window openings that make the plan easy to read. The setting is open and handsome, with hills and farmland around it.
It works well as part of a Kilmartin-area day out, especially if you are already exploring standing stones, cairns, and early medieval sites. The castle is usually a short uphill walk from the road, so it feels a little more discovered than delivered. In wet weather, expect slick grass and bring proper shoes.