They appear as low, horseshoe-shaped mounds, typically dark with charred and fire-cracked stone, and they cluster near water. The one at Faheens in County Mayo is a quiet example of a type that was once, it seems, a routine feature of Bronze Age life.

A fulacht fia, broadly speaking, is a cooking site. The standard interpretation is that a trough, often timber-lined, was dug into the ground near a water source and filled with water. Stones were heated in a nearby fire and then dropped into the trough to bring the water to a boil, after which meat could be cooked. The cracked and shattered stones, made brittle by repeated heating and cooling, were discarded to the sides of the pit, building up over time into the characteristic mound that survives today. The process is surprisingly efficient; experimental archaeology has shown that a decent-sized trough can be brought to a rolling boil in under half an hour using this method. Most fulachtaí fia date to the Bronze Age, roughly 2000 to 500 BC, though some continued in use into the early medieval period. Their precise social function is still debated, with some researchers suggesting uses beyond cooking, including brewing or bathing. The example at Faheens sits within a county that has no shortage of prehistoric monuments, Mayo's boggy and often undisturbed landscape having preserved a remarkable number of them.