It is, in fact, the remains of a fulacht fia, one of the most common yet persistently mysterious monument types in the Irish archaeological landscape.

A fulacht fia is essentially a burnt mound, the accumulated debris of repeated prehistoric cooking or hot-water activity. The typical setup involved a trough dug into the ground near a water source, stones heated in a fire, and those stones dropped into the water to bring it to a boil. Over time, the stones fractured and became useless, and the cracked, fire-blackened fragments were piled to the side, forming the characteristic horseshoe-shaped or spread mound that survives today. Thousands of these sites are known across Ireland, mostly dating to the Bronze Age, and they tend to cluster near streams or marshy ground precisely because a reliable water supply was central to however they were being used. The one at Knockahorrea follows this pattern exactly, sitting on the western bank of a stream, its burnt material still spreading beneath the grass after perhaps three or four thousand years.