It measures roughly four and a half metres across and rises only twenty centimetres at its highest point, partially overgrown and easy to miss entirely. What it represents, however, is one of the most common and quietly fascinating monument types in the Irish archaeological landscape: a fulacht fia, the remains of a prehistoric cooking site.

Fulachtaí fia are found in their thousands across Ireland, typically in low-lying or waterlogged ground close to a water source. The basic method involved heating stones in a fire, then dropping them into a water-filled trough to bring it to a boil, likely for cooking meat. The crescent or horseshoe-shaped mounds that survive today are composed almost entirely of the shattered, fire-cracked stones discarded after use, built up over repeated episodes of cooking across what may have been centuries. The example at Knocknagoul fits this pattern closely: its position in marshy ground is characteristic, and the burnt material forming the mound is the accumulated debris of those ancient fireside gatherings. Most fulachtaí fia date to the Bronze Age, roughly 2000 to 500 BC, though some were used earlier or later.