This is a fulacht fia, a type of prehistoric burnt mound found in enormous numbers across Ireland, and one of the most quietly abundant monuments in the Irish landscape. The mound measures ten metres in length and rises to about 0.8 metres at its highest point, with a central depression that hints at the trough once dug at the heart of the structure.

Fulachtaí fia, the plural form, are generally understood to be the remains of ancient outdoor cooking sites, most commonly dated to the Bronze Age, though some examples span a wider period. The typical method involved heating stones in a fire until they were intensely hot, then dropping them into a water-filled trough to bring it to a boil. The stones, cracked and spent after repeated heating, were discarded to the sides, building up over time into the characteristic horseshoe or oval mounds that survive today. At Knocknakilla, the marshy ground to the west of the mound and the proximity of the stream would have provided exactly the kind of reliable water source these sites depended upon. A possible opening of around 2.5 metres faces northeast, which may correspond to where the trough was accessed or where material was most actively deposited during use.