And yet the geometry is precise enough to be unmistakable once you know what to look for, a near-perfect circle roughly sixty-three metres across, its proportions the product of deliberate early medieval planning rather than any accident of the landscape.

Ringforts, known in Irish as raths when formed from earthworks rather than stone, were the standard unit of rural settlement in early medieval Ireland, typically dating from somewhere between the fifth and twelfth centuries. A family farmstead would be enclosed by a raised bank, with a fosse, or ditch, dug on the outside to provide the material for that bank and to add a degree of defence. The Coolrus example follows this pattern closely. The enclosing bank rises to around 1.15 metres on its interior face and 1.6 metres on the exterior, with an external fosse roughly a metre deep and just under three metres wide. A gap of 5.6 metres in the bank on the south-east side, accompanied by a causeway across the fosse, marks what would have been the original entrance. That south-eastern orientation is common in Irish ringforts and is generally thought to reflect a preference for morning light and shelter from prevailing westerly winds. The site sits on a south-east-facing slope, so both considerations would have applied here. The record was compiled by Denis Power and uploaded to the national inventory in August 2011.

The fort sits in working pasture, so access depends on the land and any gates or boundaries in the immediate area. The interior, partially covered by overgrowth according to the survey notes, has a noticeably uneven surface, which is typical of sites where internal features such as souterrains, underground stone-lined passages sometimes used for storage or refuge, or the footings of former structures have subsided over centuries. Walking the interior carefully, particularly in lower vegetation in late winter or early spring, can make those undulations easier to read. The causeway and entrance gap at the south-east are the clearest single features to locate first, and from there the full circuit of the bank becomes apparent.