The term, loosely translated as "cooking place of the deer," refers to the crescent-shaped mounds of burnt and shattered stone that mark where Bronze Age people repeatedly heated water, most likely for cooking, by dropping fire-cracked rocks into a trough. The site at Cunnagher in County Mayo is one such monument, a quiet irregularity in the bog that most people would walk past without a second thought.

The typical fulacht fia consists of a horseshoe-shaped mound surrounding a central pit or trough, often timber-lined, which would have been flooded with water and then heated by the addition of stones taken from a nearby fire. Experiments have shown the method is surprisingly effective, capable of bringing a large volume of water to a boil within thirty minutes or so. While cooking remains the most widely accepted explanation, some researchers have proposed alternatives including use as saunas, dyeing vats, or brewing vessels. Most examples in Ireland date to the Bronze Age, roughly 1500 to 500 BC, though some sites have produced earlier or later dates. Mayo, with its extensive bogland, preserves a particularly high concentration of these monuments, the peat having protected the organic and structural remains that would otherwise have long since disappeared.