It measures 14.5 metres long, 10.5 metres wide, and stands about 0.9 metres high, with an opening 4.5 metres across facing west. What makes it stranger still is that another of its kind lies roughly 15 metres to the north, meaning two of these ancient cooking sites once operated in close proximity on the same ground.

A fulacht fia, sometimes called a burnt mound, is one of the most common prehistoric monument types in Ireland, yet the way they worked retains a certain quiet fascination. The typical arrangement involves a trough dug into the ground, a nearby water source, and a hearth for heating stones. The stones were made red-hot in the fire, then dropped into the water-filled trough to bring it to a boil, allowing large quantities of meat to be cooked without a direct flame. Over time, the used stones, which fracture and crumble with repeated heating and rapid cooling, were discarded around the trough, gradually building up the characteristic horseshoe or kidney-shaped mound that survives today. Most examples date to the Bronze Age, broadly between 1800 and 800 BC, though some are earlier or later. The paired arrangement at Knocklagh is relatively unusual; whether the two sites were in use simultaneously or represent activity at different periods is not recorded, but their proximity suggests this particular patch of north Cork was a productive and repeatedly visited spot for prehistoric communities.