It is made of burnt stone and charcoal-stained soil, the accumulated debris of repeated prehistoric cooking fires, and it measures nearly nineteen metres across its longest axis and rises to about one and a half metres at its highest point. The opening of the horseshoe, almost five metres wide, faces north-northwest, and a modern field fence cuts through the mound on its south-eastern side, a reminder of how casually ancient features can be bisected by working farmland.

A fulacht fia is a type of prehistoric cooking site found in great numbers across Ireland, typically located near water or, as here, in boggy ground that would have provided a ready supply. The usual method involved heating stones in a fire and dropping them into a trough of water to bring it to a boil, a process that gradually shatters the stones and produces the characteristic mounds of cracked, fire-reddened material that survive today. The Mountkeeffe example is not an isolated one; it belongs to a cluster of three such sites in the immediate area, which suggests the location was used repeatedly and perhaps by a settled community over a long period. Concentrations of fulachta fiadh like this are not uncommon in Ireland, and they hint at organised, recurrent activity rather than casual or one-off use. Most examples date to the Bronze Age, broadly speaking the period between roughly 2000 and 500 BC, though some sites have produced earlier or later dates.