It measures roughly six metres north to south and five metres east to west, rising only about forty centimetres above the surrounding ground. That modest profile disguises what it actually is: a fulacht fia, one of the most common yet least-understood monument types in the Irish landscape.

A fulacht fia is a burnt mound, the accumulated debris left behind after repeated cycles of heating stones in a fire and plunging them into a water-filled trough to bring it to the boil. The characteristic shape here, a horseshoe or crescent of scorched and shattered stone, with the open end facing east, is entirely typical of the form. These sites date mostly to the Bronze Age, roughly 1500 to 500 BC, and their purpose has been debated for decades. Cooking is the most widely accepted explanation, though brewing, hide-working, and even communal bathing have all been proposed. What is consistent is the method: the mound builds up over time as cracked, heat-spent stones are cleared from the trough and piled to either side, eventually creating that distinctive curved bank of dark, charcoal-flecked material. At Cappagh, the mound remains unexcavated, so the details of what went on here are held in the ground rather than in any record. A separate enclosure lies approximately a hundred metres to the west-south-west, suggesting this part of the hillside saw sustained activity during prehistory rather than a single isolated episode.