Tomen-y-Cefnlloer is a ditched mound, set towards the west end of an east-west ridge, with steep slopes on the north and south, c.27-28m in diameter and 4.2m high, having a somewhat irregular summit, c.10m by 8.0m. On the east is a scarped bailey platform, c.18m by 22m, there is a further possible platform to the west.
