What gives it away is the scarp, a steep-sided bank cut into the ground rather than built up from it, running around the roughly circular interior and reaching about 1.3 metres in height along its southeastern to north-northwest arc. On the eastern side, a field boundary has absorbed part of the enclosure, folding the ancient feature into the more recent geometry of the landscape.

This is a rath, the Irish term for a ringfort, the most common monument type in the Irish countryside. Ringforts were enclosed farmsteads, typically from the early medieval period, roughly the fifth to twelfth centuries, in which a family and their livestock sheltered within a bank and ditch or, as here, a scarp cut from the natural slope. The one at Cooranuller shows a practical adaptation to its setting: the interior has been deliberately raised on the southern and western sides to level out the hillslope, so that the usable ground within the enclosure would have sat more or less flat. It is a small detail, but it speaks to considered construction rather than opportunistic use of the land. The rock outcrop breaking through the hillock nearby would have made the site visible for some distance, a consideration that may well have influenced its placement.