This is a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland, typically identified by the characteristic horseshoe-shaped mound of shattered stone left behind after repeated cycles of heating rocks and plunging them into water-filled troughs. The Coolmucky example measures roughly 17 metres along its longest axis and rises to about 0.8 metres, sitting approximately 20 metres to the north-west of a medieval moated site, with the stream that feeds that moat running between the two.

The antiquary John Windele visited and recorded the site in 1849, describing it as a fine follock, which was the local term then in use, "a large round mound of considerable circumference which stands within a few paces of the entrance [to the moated site], the stream which fills the moat flowing between." What makes Windele's account particularly interesting is that he did not stop at one. He noted a fulacht fiadh in the next field to the north-west, and a third in the field beyond that. Those two additional sites remain unlocated today, suggesting that this corner of Coolmucky once held a cluster of prehistoric activity, perhaps drawn repeatedly to the same reliable watercourse over generations. The proximity to the later medieval moated site, a type of fortified enclosure surrounded by a water-filled ditch common in Ireland from the thirteenth and fourteenth centuries, is probably coincidental, though it is a reminder of how the same practical features of landscape, steady water, firm ground, drew people back to the same places across very different eras.