This is a fulacht fia, a type of ancient cooking or processing site found in enormous numbers across Ireland, typically identified by the distinctive kidney or horseshoe-shaped mound of burnt and cracked stone that accumulates when fire-heated rocks are repeatedly plunged into water-filled troughs. The mound at Knockduff measures roughly ten metres by eight, rising only about thirty-five centimetres above the surrounding ground, its modest profile easily mistaken for a natural rise in the land.

The site's proximity to a stream is entirely characteristic of the type. Fulachtaí fia, as they are known in the plural, consistently appear near reliable water sources, since the process depended on keeping a wooden or stone trough continuously supplied. The burnt mound here is cut by a shallow furrow, a small scar in an already understated monument. What gives the Knockduff site an additional layer of interest is that a second fulacht fia lies approximately two hundred metres to the east-southeast, suggesting that this stretch of the North Cork landscape saw repeated or sustained use during the prehistoric period. Whether the two sites were contemporary with one another, or represent activity from different phases separated by generations, is not something the surface evidence can answer.