Caistel Dubh nan Cliar, the Black Castle of the Minstrels, stands on the Ormsaigbeg shore below Ian Cameron's croft. The coastline there is a low cliff line broken by small gorges down which rills of water flow, places of wildflowers in summer. The 'castle' is built against the western side of a natural rock outcrop on top of a small, steep-sided knoll, it's flanks covered with rubble that have fallen from the structure. Some of the walls are cemented, and the roof appears to have been formed of large slabs of rock.
The Royal Commission on the Ancient and Historical Monuments of Scotland categorise it as a 'Tower House' and date it as 16th century. They suggest that it had two storeys, and that it might have served as 'an outpost of Mingary Castle'.
For several reasons, it seems to me highly unlikely that it was a fortification. No more than two or three soldiers could have occupied it, and even they would have found life rather cramped. Further, it is hardly in a good defensive position - the cliff top to it's immediate west, from which the photo below was taken, directly overlooks it. There are far better sites, at superior elevation and with sounder natural defences, within a short distance - for example, the cliff top at Maol Buidhe, which offers views across the Sound and as far west as Tiree.
MEM Donaldson, who travelled in this area of the Highlands in the early years of the 20th century, suggested that it might have been the "abode of some 'minstrel' of solitary habit" who, in celebration of his skills, called his place a 'castle'. Perhaps he wasn't that good. In fact, perhaps he was so terrible that his laird built him a 'castle' and sealed him into it.