The ringfort at Coolnagillagh, sitting on a north-east-facing slope about three hundred metres west of the Owenbaun River, is rather more deliberate than that. A rath, as this type of enclosure is known in Irish, is an early medieval farmstead, typically dating from roughly 500 to 1000 AD, enclosed by one or more earthen banks and ditches. The people who built and lived in such places were farmers and landowners, and the earthworks that survive around them represent the boundaries of domestic life rather than any grand military design.

The engineering here is quietly intricate. The main bank, which reaches about a metre in height on the interior, runs from the north-north-east around to the south, with a fosse, meaning a ditch, sitting between it and an outer bank that stands slightly higher at around 1.2 metres. A further outer fosse, half a metre deep, runs to the north-west. The entrance faces north-east, approached by a causeway across the ditches, and the gap in the outer bank, roughly four metres wide, preserves faint traces of stone facing at its edges, suggesting that whoever built the entrance was giving it some definition and perhaps a degree of permanence. Inside, the ground is saucer-shaped, dipping gently downward toward the north-east, which may have been a deliberate choice to assist with drainage on what is already a sloping site.