This is a fulacht fia, a type of Bronze Age cooking site found in considerable numbers across Ireland, typically identified by exactly this combination: a crescent-shaped mound of heat-shattered stones, charcoal-darkened soil, and proximity to water. The basic method involved heating stones in a fire, dropping them into a water-filled trough to bring it to the boil, and using the resulting heat to cook meat. Over repeated use, the cracked and spent stones were raked aside, gradually building up the characteristic mound that survives millennia later.

The Derrymihin example measures roughly nine metres along its northwest to southeast axis and five metres across, rising only about half a metre from the surrounding ground. Its mouth, around two and a half metres wide, opens to the southwest, oriented towards the stream that would have supplied the water essential to the whole operation. The mound is composed of the usual material: stones fractured by repeated heating and cooling, bound together with soil darkened by charcoal. What makes the site particularly notable is its company. Two further fulachtaí fia lie within easy distance, one approximately sixty metres to the east and another around thirty metres to the northeast. Whether this clustering reflects seasonal activity, communal use across generations, or simply the practical advantage of a reliable water source drawing people back repeatedly, the three monuments together suggest this boggy slope was a place of deliberate, recurrent significance during the Bronze Age.