The one recorded at Callow in County Mayo is a quiet example of a site type that appears almost everywhere and yet still generates genuine debate among archaeologists. A fulacht fia typically survives as a horseshoe-shaped or kidney-shaped mound of fire-cracked stone and dark, charred soil, usually positioned close to a natural water source. The working theory, now fairly well supported by experiment, is that these were outdoor cooking sites: stones were heated in a fire, dropped into a water-filled trough, and used to bring the water to a boil. The process is efficient, and replicated experiments have shown that a significant volume of water can be brought to a boiling point in surprisingly little time.

Most fulachtaí fia date to the Bronze Age, roughly between 1500 and 500 BC, though some have produced earlier or later dates. The sheer number of them, estimated at over four thousand in Ireland alone, suggests they were an ordinary feature of daily or seasonal life rather than anything ceremonial or exceptional. What made them accumulate so visibly in the landscape is the waste product: shattered, heat-fractured stone that was discarded after each use, building up over repeated firings into the low mounds that survive today. The Callow example, sitting in the low, wet ground of north-west Mayo, fits the typical pattern of a monument that is easy to overlook and difficult to date precisely without excavation.