What erodes out is not soil in any ordinary sense but a dense mass of heat-shattered limestone fragments bound in charcoal-black earth, the accumulated refuse of repeated, ancient fire-and-water activity. The mound is modest in scale, roughly sixteen metres across at its longest axis and no more than a metre and a half high along its western arm, yet its shape and composition identify it unmistakably as a fulacht fia.

A fulacht fia is a type of prehistoric cooking or processing site found in enormous numbers across Ireland, typically Bronze Age in origin. The usual method involved heating stones in a fire until they were intensely hot, then dropping them into a water-filled trough to bring the water rapidly to the boil. The stones, cracked and useless after a single heating, were discarded to the side, building up over time into the characteristic mound that survives today. At this site on Aghawinnaun, the relationship between mound and water source is unusually direct. A central U-shaped depression, opening to the south-west, aligns almost exactly onto the spring that issues from the base of the bedrock scarp behind the terrace. The spring now flows past the mound to the north-north-west, but its proximity to the hollow at the mound's centre suggests the two were once functionally connected. The site was already noted on the 1916 Ordnance Survey six-inch map, marked as a small circular feature with a well symbol immediately to its south-west, meaning its presence was recorded long before modern archaeological classification caught up with it.

The mound sits on a narrow natural terrace, sheltered to the south-east by a low scarp of exposed bedrock. Large stones and boulders protrude from the south-western arm of the mound, hinting at structural elements beneath the surface. Where erosion has stripped back the thin sod, the burnt limestone and charcoal-rich matrix are plainly visible, giving the site a raw, legible quality that many such monuments, now buried entirely under farmland, no longer possess.