These ancient cooking sites, found in their thousands across Ireland, are among the most common prehistoric monuments in the country, yet they remain largely unknown outside archaeological circles. The typical fulacht fia consists of a horseshoe-shaped or kidney-shaped mound of burnt and shattered stone, accumulated beside a trough or pit that would once have been filled with water. The working theory, supported by experimental archaeology, is that stones were heated in a nearby fire and then dropped into the water-filled trough to bring it to a boil, allowing meat to be cooked. The characteristic crescent mound is simply the discarded pile of stones, cracked and spent from repeated heating and cooling.

Most fulachta fia date to the Bronze Age, roughly between 1500 and 500 BC, though some have earlier or later origins. They tend to appear near water sources, streams, or boggy ground, which provided the necessary supply for the trough, and many have been preserved beneath peat, emerging only when bogs are cut or drained. Mayo has a considerable concentration of these sites, the county's wet, low-lying ground having offered both the practical conditions their builders required and, later, the preservation conditions that kept them intact. The site at Lack is one of many recorded across the townlands of the county, each one a small, durable trace of everyday Bronze Age life rather than anything ceremonial or monumental.