It measures 7.6 metres north to south and 3.2 metres east to west, rising about a metre in height, and beneath its grassy surface lies a compressed mass of burnt material, the accumulated debris of prehistoric cooking. This is a fulacht fia, one of the most common yet persistently mysterious monument types in the Irish archaeological landscape.

Fulachtaí fia are generally understood to be ancient cooking sites, though the term itself is older than the science used to study them. The typical method involved heating stones in a fire, then dropping them into a water-filled trough to bring it to a boil, a process that cracked and shattered the stones over time. The discarded burnt and broken stone gradually accumulated into the horseshoe or oval mounds that survive in their thousands across Ireland, most dating to the Bronze Age. At Gearhanagoul, the proximity to a stream would have provided a ready water source, a characteristic shared by the vast majority of these sites. The western face of the mound has been eroded, exposing some of the dark, burnt material inside, giving a rare unmediated glimpse of what these features are actually made of.