That density alone makes Knockagolig unusual, even by the standards of Irish prehistory, which has no shortage of fulachtaí fia. A fulacht fia is a burnt mound, the remains of an ancient cooking or processing site where stones were heated in fire and dropped into a water-filled trough to bring it to the boil. What gets left behind is a characteristic horseshoe-shaped heap of cracked, fire-blackened stone, and the one recorded here is a reasonable specimen of the type: roughly 25 metres along its longer axis, 19 metres across, and still standing about 40 centimetres above the surrounding ground. Its opening faces north-northwest, towards the wetter, lower ground, which is exactly where you would expect it, since proximity to a reliable water source was the whole point.

The mound sits on a break in a northwest-facing slope, right at the boundary where wet ground to the north gives way to drier, rising terrain to the south. That kind of transitional ground, useful for drainage and water access at once, was a preferred location for these sites across Bronze Age Ireland. The mound has not escaped interference: two forestry trenches, each roughly 85 centimetres wide and 80 centimetres deep, were cut through it on a north-northwest to south-southeast axis, bisecting the eastern arm and catching the edge of the western one. Three more fulachtaí fia lie within roughly 200 metres, to the southwest and south-southwest. A researcher named Bowman, writing in 1934, recorded four such sites in the townland and associated them with land then held by Maurice Culhane, Mr Cagney, Thomas Field, and Patrick O'Regan respectively. Whether these four named parcels correspond exactly to the four monuments as mapped is not certain, but the overlap is striking enough to suggest Bowman was recording the same cluster that survives today, at least in part.