At Britfieldstown in County Cork, one such site sits in boggy ground on a north-facing slope, presenting itself as little more than a low, irregular mound of burnt material. That modest appearance is deceptive. A fulacht fia is essentially the remains of a prehistoric cooking place, where stones were heated in a fire and then dropped into a water-filled trough to bring it to the boil. Over repeated use, the cracked and shattered stones were raked out and piled to the side, eventually forming the horseshoe-shaped or irregular mounds that survive today.

The boggy, waterlogged setting at Britfieldstown is entirely typical. Fulachta fiadh are almost always found near a reliable water source, whether a stream, spring, or naturally wet ground, and the saturated conditions that make such spots uncomfortable for farming are precisely what has preserved these sites for so long. The burnt and fragmented stone that constitutes the mound, often a dark reddish-brown from the scorching, can look unremarkable to the untrained eye, easily mistaken for a natural hummock or a patch of disturbed ground. Most examples in Ireland date broadly to the Bronze Age, though some have produced dates ranging across a wide span of prehistory, and their precise function has attracted considerable debate, with suggestions ranging from cooking and food preparation to bathing or textile processing.