What draws the eye is the asymmetry of its enclosing bank: at the southern arc it rises only 2.2 metres above the outer ditch, but swing round to the north and that same bank climbs to 4.3 metres, its base widening from 4.7 metres to a full 6 metres. The ditch, or fosse, runs around the outside at roughly 4 metres wide, still measurable at nearly a metre below the surrounding ground level in places. Two gaps break the circuit at the north-east and north-west, which may represent original entrances or later breaches.

This is a univallate rath, meaning a ringfort enclosed by a single bank and ditch rather than the multiple concentric rings found at more elaborate sites. Raths are among the most common early medieval monument types in Ireland, typically associated with farmstead enclosures of the period roughly between the fifth and twelfth centuries, and the Iveragh Peninsula holds a considerable concentration of them. What makes Derrymore worth pausing over is the structure preserved inside. On a raised area in the southern half of the interior stand the remnants of a stone-built rectangular building, measuring 5.8 metres by 2.8 metres internally, its walls still surviving to around 0.6 metres in height. The combination of a defined interior building alongside the earthwork itself gives a rare, if fragmentary, sense of the enclosed domestic space these monuments once contained. The bank along the northern sector also carries a notably high stone content within the earth, a local variation that likely reflects the rocky terrain of the surrounding mountains.