What looks from a distance like a slightly raised circle of pasture turns out, on closer inspection, to be a carefully engineered enclosure, its perimeter formed by a scarped bank that still stands 1.7 metres high on its north-western to eastern arc. The interior dips gently inward towards the centre, a subtle bowl shape that only becomes apparent once you are standing inside it.

Ringforts, known in Irish as raths when constructed from earthen banks rather than stone, were the standard farmstead enclosure of early medieval Ireland, used roughly between the fifth and twelfth centuries. Thousands survive across the country in varying states of preservation. The Coolrus example is roughly circular, measuring 35 metres north to south and 28.7 metres east to west. The enclosure is defined by two scarped edges of differing heights, the more substantial running from the north-west around to the east at 1.7 metres high and nearly five metres wide, the lesser arc measuring 0.75 metres high and 4.4 metres wide. An external fosse, the shallow ditch that would originally have helped define and defend the perimeter, runs along the eastern side, though it is now only 0.35 metres deep and two metres wide. A causeway entrance survives at the southern end, 3.6 metres across, wide enough to have admitted livestock as well as people. The site was recorded by Denis Power, with notes uploaded in August 2011.

The fort sits on a gentle east-facing slope, currently under pasture, and the approach across open farmland means the earthworks read clearly against the slope once you know what to look for. The causeway entrance at the south is the clearest starting point for understanding the layout. The eastern to south-eastern section of the perimeter is the most obscured, buried under dumps of topsoil and field-clearance stones accumulated over generations of agricultural tidying, now covered in overgrowth. The rest of the circuit is considerably cleaner. Walking the inner edge of the bank gives the best sense of the enclosure's original scale, and the slight downward gradient of the interior floor becomes noticeable underfoot in a way it does not from any exterior vantage point.