The one at Rathedmond, on the outskirts of Sligo town, is a quiet example of a type that continues to puzzle archaeologists. A fulacht fia typically survives as a horseshoe-shaped mound of fire-cracked stone and charcoal-blackened earth, usually found close to a water source. The mound is the accumulated debris of repeated use over time, the broken and discarded stones that were heated in a fire and then dropped into a water-filled trough to bring it to the boil.

The purpose of these sites has been debated for decades. For a long time the dominant theory held that they were outdoor cooking places, used during the Bronze Age, roughly between 2000 and 500 BC, by hunters or seasonal travellers who needed to prepare meat in the field. More recent experiments and arguments have suggested other possibilities, including brewing, hide-working, or bathing. No single explanation has been universally accepted, and it is likely that different sites served different purposes at different times. What is consistent is the method: the trough, the heated stones, the gradual accumulation of spent material around the pit. At many sites across Ireland the waterlogged conditions that made a location suitable in the first place have also helped preserve organic material within the mound, giving excavators a rare window into prehistoric activity.