This is a rath, the Irish term for a ringfort, a type of enclosed farmstead built in early medieval Ireland, typically between the sixth and tenth centuries. Thousands of them survive across the country, yet each one carries its own quiet particularity, and this one at Coolbaun is no exception.

The structure measures roughly 31 metres across its east-west axis, defined by a bank of earth and stone that has grown over with vegetation across much of its circuit. The bank itself is substantial, reaching 5.4 metres in width, with an internal height of around 1.5 metres and an external height of 1.1 metres. The interior ground slopes gently southward, and the whole enclosure faces a southern aspect, a detail that would have mattered greatly to whoever chose this spot, since a south-facing slope catches more light and warmth. A narrow gap of about one metre on the north-western side has been identified as a possible original entrance, though a similar gap on the south-western side appears to be a more recent cattle break, the kind of informal opening that farmers create over centuries of working the land around these ancient boundaries. Field boundaries on three sides of the bank, at the north-east, south-east, and south-west, press up close against it, a reminder of how the agricultural landscape has continued to reorganise itself around these older shapes rather than erase them.