This is a rath, the Irish term for a ringfort, the most common archaeological monument type in Ireland. Thousands were built, mostly during the early medieval period, as enclosed farmsteads for a single family and their livestock. What is easy to overlook, standing inside one, is just how deliberate the engineering was: a raised bank, a fosse or external ditch to increase the effective height of the defences, and a controlled entrance point. At Coolageela, that entrance survives as a gateway in the bank to the south-south-east, with a path running from it across the interior toward a levelled section of bank to the north-north-east.

The monument measures approximately 38 metres on its longer axis and just over 36 metres across, making it a reasonably substantial example of its type. The bank is stone-faced in places on its outer side, a detail that speaks to the effort originally invested in its construction. A fosse, the shallow external ditch that would have added both a physical and a psychological barrier, survives to the west as a gentle slope down to the base of the bank, though it is less pronounced than it might once have been. The interior itself is not flat; it drops away from the centre toward the north-north-east and rises slightly near the eastern bank, giving the enclosed space a subtle topography. Farm activity has taken its toll on the north-east to east section of the bank, where a building has cut into the outer face, and mature deciduous trees have been planted along the eastern and northern arc, which will have further disturbed the ground over time.