They appear as low, kidney-shaped or crescent mounds of fire-cracked stone and dark, charcoal-flecked earth, typically found close to a water source. The one at Kinlough in County Mayo is one such survival, a low accumulation of heat-shattered rock that marks a spot where people repeatedly built fires and plunged hot stones into water-filled troughs, probably during the Bronze Age.

The mechanics of a burnt mound are straightforward enough once explained. Without metal vessels capable of withstanding direct flame, prehistoric people heated stones in a fire and dropped them into a wooden or stone trough filled with water, bringing it rapidly to the boil. The stones, cracked and spent after a single use, were raked aside, and over many visits the discarded material built up into the characteristic mound we recognise today. What the hot water was actually used for remains genuinely open: cooking, bathing, industrial processes such as working hides, or communal gathering have all been proposed, and the honest answer is that no single explanation has settled the debate. The Irish term fulacht fiadh, sometimes translated loosely as cooking pit of the deer, is widely used for these sites, though its original meaning is disputed. Mayo has a considerable concentration of them, tucked into boggy ground and river margins across the county, most of them unremarked by any passing traffic.