They appear as low, horseshoe-shaped mounds, typically found beside streams or marshy ground, and are thought to represent ancient cooking or processing sites where water was heated by dropping fire-scorched stones into a trough. The stones crack and shatter with repeated use, and it is this accumulation of burnt, fragmented rock that forms the mound itself. One such site survives at Eskeragh in County Mayo, a modest but genuine trace of prehistoric activity in the townland.

Fulachta fia are broadly dated to the Bronze Age, roughly 1500 to 500 BC, though some examples fall outside that range. The name itself is from Old Irish and is sometimes translated loosely as "cooking place of the deer", though the precise original meaning is debated. What is consistent across excavated examples is the method: a wooden or stone-lined trough, a hearth nearby, and the repeated cycle of heating stones and plunging them into water. Experiments have shown the technique can bring a substantial volume of water to the boil surprisingly quickly. Whether the sites were used for cooking meat, processing hides, bathing, or some combination of these remains an open question among archaeologists. The example at Eskeragh adds one more point to the distribution of these features across the west of Ireland, a region where they occur with particular frequency.