These are fulachtaí fia, a type of ancient cooking site found across Ireland in enormous numbers, typically dating to the Bronze Age. The standard interpretation holds that they functioned as outdoor boiling places: a trough, often timber-lined and sunk into the ground, was filled with water, then heated by dropping fire-cracked stones into it. The burnt and shattered stones were raked out after use and gradually accumulated into the characteristic horseshoe shape around the trough's edge. At Knocknanagh, that accumulation has produced something unusually substantial.

The main mound measures sixteen metres east to west and thirteen metres north to south, rising to a height of two metres, with an opening six metres wide facing north-west. Immediately to its south-west sits a smaller companion mound, twelve metres by eight, its opening oriented to the east-north-east. The two structures are distinct, with their openings facing in different directions, suggesting they may have operated independently rather than as a single installation. A third fulacht fia lies roughly thirty-four metres to the north, which means this corner of Knocknanagh Commons preserves at least three of these monuments in relatively close association. Whether that reflects repeated use of a favoured location over time, or something more organised, is not something the surface evidence alone can answer. What it does suggest is that this was not a casual or one-off use of the landscape.