Beneath the turf lies a mound of burnt and fire-cracked stone, the characteristic signature of a fulacht fia, a type of prehistoric cooking or heating site found in great numbers across Ireland. The mound sits at the foot of a west-facing slope, with a stream running to the north, an arrangement that is almost diagnostic of the type: fulachtaí fia are almost always found close to running water.

A fulacht fia typically worked by heating stones in a fire, then dropping them into a water-filled trough to bring the water rapidly to a boil. The discarded, shattered stones accumulated over repeated use into the horseshoe-shaped or spread mounds that survive today. Most examples date to the Bronze Age, roughly 1500 to 500 BC, though some are earlier or later. The sheer number of these sites across Ireland, and the labour involved in their repeated use, suggests they were a regular fixture of prehistoric life, though whether they were used primarily for cooking, bathing, textile processing, or some combination of purposes remains a matter of ongoing debate among archaeologists. The example at Lissanoohig presents itself modestly: a grass-covered spread of burnt material in ordinary pasture, offering no obvious drama to a passing eye.