Sitting within that bowl is an oval mound of burnt stone, roughly fourteen and a half metres east to west and just half a metre high, the kind of feature that most people would walk past without a second glance. This is a fulacht fia, a type of prehistoric cooking or processing site found in great numbers across Ireland, typically identified by exactly this signature: a low, horseshoe-shaped or oval spread of heat-shattered stone, accumulated over repeated use of a nearby water source. The stones were heated in fire and dropped into a water-filled trough to bring the liquid to a boil, shattering in the process, and the discarded fragments built up into the mound that survives today.

At Knockroe, the mound is partially obscured to the south by cleared stone and encroaching bushes, but along the northern edge some possible revetting stones are still visible, suggesting the mound may once have been deliberately edged or contained. Where the upper surface has been disturbed by livestock, the burnt stone composition is exposed directly underfoot. Sixteen metres to the north-east lies a holy well, a proximity that is not entirely surprising. Fulachtaí fia consistently favour low, wet ground close to reliable water, and holy wells in Ireland frequently occupy the same kinds of marginal, moisture-gathering spots that attracted activity in prehistory. Whether any direct relationship existed between the two features at Knockroe is unknown, but the clustering of water-associated places in this hollow gives the site a quiet layered quality, different periods of human attention drawn to the same patch of ground for reasons that may not have been entirely different from one another.