The feature is D-shaped, roughly 23 metres by 16 metres, and defined by a low bank and a fosse, which is a shallow defensive ditch running along the outer edge. What makes it curious is its position: not a standalone monument, but a subdivision or annexe tucked inside the arc of an already-enclosed space.

Ringforts, built predominantly during the early medieval period in Ireland, were circular or near-circular enclosures typically defined by earthen banks and ditches, used as farmsteads or places of settlement and occasional refuge. The presence of a secondary enclosure within one is not unheard of, but it is far from the norm. Such internal divisions could have served a range of functions, separating livestock from living quarters, providing an inner sanctum for a higher-status occupant, or simply reflecting a later phase of activity on an already-occupied site. Without excavation, the specific purpose of this D-shaped annexe at Kill remains open, which is part of what makes it interesting rather than merely decorative.