The monument consists of the remains of a small castle, possibly originally a dun, situated on an islet off Calvay, on the S side of Loch Boisdale.
The islet on which the castle sits was formerly connected to Calvay by a causeway, but this has now almost completely gone. On the landward side a curving wall of irregular thickness and of drystone masonry appears to be the earliest element of the remians: it may be part of a dun. The W, N and NE sides of a polygonal enclosure are
formed by badly mortared walls of rough rubble, in places
incorporating substantial stretches of earlier, unmortared, walling.
The fortification has maximum overall dimensions of 30m SW-NE by 20m. A number of gun-slits are evident, particularly on the W side. There are two main internal buildings, both abutting and incorporating the outer wall. On the SW corner a small square structure some 4m by 4m externally may have been a low tower overlooking the approach from Calvay. On the N side is a bicameral rectangular block some 13m by 6m externally, possibly formed by the eastward extension of a smaller structure.
The remains are too ruinous to be certain about the
phasing of construction. The area to be scheduled consists of the whole of the small islet, above the edge of the tidal rocks: this coincides with the enclosure and its interior, as marked in red on the accompanying map.