The enclosure at Castlegar is barely legible now, its circular form roughly 26 metres across, surviving only as a low scarp that marks the central area and, to the south-south-east, traces of a shallow fosse and counterscarp. A fosse is simply a ditch, typically dug as part of a defensive or boundary arrangement, with the counterscarp being the outer face of that ditch. Together they hint that an outer bank may once have reinforced the whole structure, though little of it remains.

The site sits on land that was formerly part of Castlegar Demesne, the managed estate landscape that once surrounded Castlegar House. Whatever the enclosure's original purpose, whether a ringfort-type settlement, a stock enclosure, or something else entirely, the demesne's later land use has left its mark. A road now cuts directly across the northern sector, erasing part of the circuit, while the southern edge has fared somewhat better. A level patch of ground at the south-south-west is thought to represent the original entrance, which would have been a deliberate gap or causeway across the boundary earthworks, a feature that often survives in enclosures of this kind even when the banks themselves have largely disappeared.