This is a fulacht fia, a type of prehistoric cooking site found in remarkable numbers across Ireland. The basic principle was straightforward: stones were heated in a fire, dropped into a water-filled trough, and used to bring the water to a boil for cooking meat. The process produces a distinctive debris of fire-cracked stone and charcoal, which accumulates around the trough in the characteristic horseshoe or kidney shape that survives here at Knockacummer.

This particular example measures roughly 13.8 metres in length and 8.5 metres in width, rising to about 0.9 metres at its highest point. The opening of the horseshoe, some 5.7 metres wide, faces to the north-west, and the south-west arm of the mound is noticeably lower than its counterpart, possibly through later disturbance or uneven accumulation during use. What makes the spot especially notable is that a second fulacht fia lies immediately to its north, suggesting repeated or sustained prehistoric activity along this particular stretch of stream. The proximity to water is no coincidence; a reliable water source was essential to the whole operation, and Irish fulachta fiadh are almost invariably found close to streams, rivers, or boggy ground.