Castell is a hill of glacial drift located immediately to the sound of Tan-y-Castell farm. It is roughly 25?30ft (7.62?9.14m) in height, with an oval, relatively flat summit around 90ft (27.43m) by 110ft (33.53m) in diameter, which gently slopes to the south east. The structure may possibly be largely artificial, but the natural hill has been scarped to give it its current form. The northern and north-western slopes are steeply scarped and slope towards a narrow road at the bottom which has almost certainly been cut into the mound itself. The other sides have been scarped more gently, with a terrace around most of the south of the mound, likely an external ditch and outer bank. A modern field wall runs around the south and west sides while a retaining wall over 1m high runs on the west side. A quarry has cut into the northwest side of the mound substantially, showing it to be largely composed of sand and gravel which appears to be natural in this area of the mound.

The site is generally described as a motte but is somewhat atypical. It resembles a medieval ringwork but may date from significantly earlier as it is somewhat similar to Irish raised raths and small Iron Age forts.

(Sources: Cadw Registered File, CAM 1/1/3658; Cadw Scheduled Monument Record for CN197; Cadw SAM Full Report for CN197; Gwynedd Archaeological Trust, HER, PRN 7; RCAHMW, Inventory of the Ancient Monuments in Caernarvonshire, Vol. II: Central (London: Her Majesty's Stationary Office, 1960), p. 175.
A.N. Coward, RCAHMW, 16.01.2019