It is a fulacht fia, a type of prehistoric cooking site found in extraordinary numbers across Ireland, and one of the more quietly fascinating categories of archaeological monument on the island. The typical fulacht fia consists of a horseshoe-shaped mound of fire-cracked stone surrounding a trough, usually timber-lined, which would have been filled with water. Stones heated in a nearby fire were dropped into the trough to bring the water to a boil, a method capable of cooking large quantities of meat. The mounds we see today are essentially the accumulated debris of those heated, shattered stones, discarded after use over many generations.

Fulachtaí fia, as they are known in the plural, date mostly to the Bronze Age, roughly 1500 to 500 BC, though some examples extend into the early medieval period. They tend to cluster near water sources, streams or boggy ground, which provided both the water for the trough and the anaerobic conditions that have helped preserve the organic material within them for millennia. Mayo has a significant concentration of these sites, as do the other western counties, where blanket bog has acted as a natural preservative across the landscape. The Lack example is one of many recorded across the county, each a small, silent trace of a cooking tradition that was once widespread and apparently very well organised.