One of them measures twelve metres along its longer axis and stands nearly a metre high, its horseshoe opening facing northwest. These are fulachtaí fia, a type of prehistoric cooking site found in their thousands across Ireland, typically dated to the Bronze Age. The standard interpretation is that a trough dug into the ground was filled with water, stones were heated in a nearby fire, and the hot stones were dropped into the trough to bring the water to a boil. The broken, fire-cracked stones were then discarded to either side, building up over generations into the characteristic horseshoe mound that survives today.

The site at Rossnashunsoge sits within a network of field boundaries, tucked into the kind of low, damp ground that fulachtaí fia consistently favour, presumably because such locations offered a reliable water supply close to the surface. The mound here is composed of heat-shattered stones mixed with charcoal-enriched soil, the residue of repeated burning episodes. Its northeastern arm has suffered some erosion, and gorse has crept across parts of the mound, as tends to happen on unimproved land left undisturbed for long enough. The proximity of the second fulacht fia, roughly fifteen metres to the southwest, is not unusual in itself. Clusters of these sites are recorded across Cork and elsewhere, suggesting that certain locations were returned to repeatedly, perhaps across several generations or even centuries.