The one at Ballygarriff in County Mayo is a quiet example of a type that continues to puzzle archaeologists despite decades of excavation and experiment elsewhere in Ireland.

A fulacht fia, in its simplest form, is a burnt mound, typically a horseshoe-shaped heap of fire-cracked stones and charcoal-blackened soil beside a trough or pit. The prevailing theory holds that water was boiled by dropping heated stones into the trough, though whether this was primarily for cooking, bathing, textile processing, or some combination of purposes remains genuinely contested. Most examples date to the Bronze Age, roughly 1500 to 500 BC, though some have produced earlier or later dates. They tend to cluster near water, and Mayo's boggy, well-watered landscape is exactly the kind of terrain where they appear with some regularity. The mound itself is the accumulated debris of repeated use, each episode adding another layer of spent, shattered stone that was discarded rather than reused.