This is a fulacht fia, a type of prehistoric cooking site found in extraordinary numbers across the Irish landscape. The typical form is a horseshoe-shaped mound of burnt and shattered stone, surrounding a trough that was once lined with timber or clay. Stones were heated in a fire and then dropped into the water-filled trough until it reached boiling point, a method efficient enough to cook a joint of meat in a matter of hours. Thousands of these sites survive across Ireland, dating broadly from the Bronze Age, roughly 1500 to 500 BC, though some examples are earlier or later.