This is a fulacht fia, a type of prehistoric cooking site found in extraordinary numbers across Ireland, with estimates running to several thousand examples nationwide. The typical form is a horseshoe-shaped mound of burnt and shattered stone surrounding a depression where a timber-lined trough once held water. The method, as best understood, involved heating stones in a fire and dropping them into the trough until the water reached boiling point, a surprisingly efficient process that experimental archaeology has repeatedly confirmed.

Fulachtaí fia, as the plural is rendered in Irish, are generally associated with the Bronze Age, roughly 2000 to 500 BC, though some sites have returned dates outside that range. The name itself is a medieval one, sometimes translated loosely as "cooking place of the deer," though whether they were used primarily for preparing food, for bathing, for textile processing, or for some combination of these remains an open question. What makes them such a conspicuous feature of the Irish landscape is the durability of the burnt stone mounds, which survive in boggy ground particularly well. Mayo has many such sites, the county's wet and peaty soils having preserved evidence that would long since have vanished elsewhere.