It is, in fact, a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, typically dating from the Bronze Age. The standard interpretation is that stones were heated in a fire, then dropped into a water-filled trough to bring it to the boil, and the shattered, heat-stressed fragments were piled up over time into the characteristic horseshoe or kidney-shaped mound that survives. This particular example measures roughly twelve metres east to west and nearly seven metres north to south, rising about half a metre above the surrounding ground, and its opening, around 1.2 metres wide, faces north onto what appears to have been a dry channel fed from a stream to the south-west, suggesting the trough was positioned to draw on that water source.

What makes the site at Derreenataggart Commons especially worth attention is not the mound itself in isolation but the density of activity it implies in its immediate surroundings. Within roughly ten metres to the north-east there is a hut site, pointing to associated habitation rather than the mound being a solitary, incidental feature in the landscape. To the south-west and west, within fifty metres, lie a second fulacht fia and a burnt mound, meaning that multiple episodes of this kind of intensive, fire-and-water activity took place in close proximity. A network of field boundaries survives in the area too, with one wall running immediately to the north of this mound. Faint traces of east-to-west cultivation ridges can still be made out on the mound's surface, a sign that the site was disturbed or reused at some later agricultural phase, after the original Bronze Age activity had long ceased.