This is a fulacht fia, a type of ancient cooking or processing site found in extraordinary numbers across Ireland, typically identified by the distinctive horseshoe-shaped mound of fire-cracked stones left behind when heated rocks were repeatedly plunged into water to bring it to the boil. The mound at Maulnahorna measures roughly ten metres in length and nearly thirteen metres across, rising only half a metre above the surrounding ground, its opening, about four metres wide, facing east.

The choice of location is typical of the type. Fulachtaí fia are almost invariably found near water, and the ground around this one is described as marshy, which would have provided the reliable water source these sites required. The standard interpretation is that a trough, often timber-lined or cut into the earth, was filled with water and heated using stones fired in a nearby hearth. The broken, heat-shattered stones accumulated over repeated use, gradually building up the characteristic mound. What exactly was being cooked, or whether some sites served other purposes such as textile processing or bathing, remains a subject of ongoing discussion among archaeologists. What is consistent is the form: that low, curved bank of blackened material, open on one side, sitting close to wet or boggy ground.