It measures fourteen metres north to south, twelve metres east to west, and stands only about sixty centimetres high. What fills it, however, is not ordinary earth but burnt material, the accumulated debris of ancient cooking or industrial activity carried out over what may have been generations.

This is a fulacht fia, a type of prehistoric cooking site found in extraordinary numbers across Ireland, with County Cork alone containing thousands of recorded examples. The typical arrangement involves a trough dug into the ground, a nearby water source, and a hearth for heating stones. Stones would be fired and dropped into the water-filled trough to bring it to a boil, and once used, the cracked and shattered stones were discarded to the side, building up over time into the characteristic horseshoe or oval mound of dark, fire-fractured material that survives today. The proximity of the Knocknagree mound to its spring is entirely consistent with this pattern; access to water was not incidental but central to the whole operation. Most fulachtaí fia date to the Bronze Age, broadly speaking the period from around 2500 to 500 BC, though some sites have produced dates extending into the early medieval period.