A fulacht fia, the most common prehistoric monument type in Ireland, is essentially an outdoor cooking place, typically identified by a mound of fire-cracked stones and dark, charcoal-rich earth left behind after repeated episodes of heating stones in a fire and plunging them into water-filled troughs to bring the water to a boil. Thousands are known across the country, most of them Bronze Age in date, and they tend to cluster near water. The Carrignafoy example sat about seventy metres west of a stream, in a field that was marshy to the east, which is precisely the kind of low, damp ground these sites seem to favour.

When archaeologist Ní Loingsigh excavated the site in 2007, the spread of burnt material measured roughly sixteen metres east to west and nine metres north to south. Beneath it lay not one trough but three, which gives the site a degree of complexity worth pausing over. The largest was a substantial subrectangular stone-lined trough on the western side, running over five metres in one direction and nearly a metre deep in places, with a stone-lined hearth immediately adjoining its northern end. A possible circular structure, about five metres in diameter, appears to have enclosed this western trough. On the eastern side of the spread, a large oval trough and a smaller, steep-sided one were separated from each other by a pair of large stones, with a shallow U-shaped channel connecting the rectangular trough to the smaller one to the east. Post-holes and stake-holes found in the vicinity suggest some kind of above-ground activity, though no coherent plan emerged from their arrangement. The only object recovered from the entire excavation was a single stone tool, possibly a hone stone used for sharpening, which underlines how thoroughly functional these sites were, used hard and left with little behind.