The one at Cunnagher in County Mayo is a quiet representative of a type that has puzzled researchers for generations. A fulacht fia typically survives as a low, horseshoe-shaped mound of fire-cracked stone and charred earth, marking the spot where, during the Bronze Age, people repeatedly heated water by dropping stones that had been superheated in a nearby fire into a timber- or stone-lined trough. The mound itself is the accumulated debris of that process, stones discarded after they cracked and became useless, building up over what may have been centuries of repeated use.

What these sites were actually used for remains genuinely contested. The most widely repeated theory is that they served as cooking places, and experiments have shown that the method works efficiently for boiling meat. Other proposals include their use as sweat houses, textile processing sites, or brewing locations. Most fulachta fia are found near water, which was essential to the process, and they cluster in low-lying, often boggy ground, which is also why so many have survived, preserved beneath layers of peat. The Mayo landscape, with its expanses of blanket bog and wetland, is particularly well populated with them. Beyond its location at Cunnagher, the specific history of this example is not fully documented in available sources.