This monument comprises the remains of a late 13th-century castle built by the Comyn Lords of Lochaber.
The building is roughly square with a round tower on each corner. The W corner tower is larger than the other three. There are gates through the walls on the NW side, facing the River Lochy, and the SE side. The walls stand to about 9m in height. Running round the SW, SE and NE sides there is a heavily silted defensive ditch which was presumably flooded. Beyond this is a slighter wall which appears to be purely 19th-century.
Recent excavation has shown earlier occupation of the site than the present upstanding remains. It also uncovered later use of the site for industrial processes in the 18th century.
The area to be scheduled is roughly rectangular. It is bounded to the N by the River Lochy, to the E by the W bank of an open drainage ditch, to the S by the fence flanking the tail race from the Lochaber Smelting Works and to the W by the fence flanking the railway line. Where this fence stops short of the river, the boundary is continued by the line of the parapet of the railway bridge. Within this area there is one principle exclusion, the building and grounds of Old Inverlochy Cottage to the SW of the Castle. This exclusion measures roughly 17m E-W by 16m N-S and is defined by but does not include the boundary of the property. Within the scheduled area are several telegraph poles, a metalled road and modern fences. These features are included in the scheduling because their alteration could be damaging to the archaeology of the site. The area to be scheduled measures approximately 160m E-W by 130m N-S at its greatest extent and is marked in red on the accompanying map.