It measures roughly eight metres north to south and just under five metres east to west, rising to less than a metre in height. What lies beneath the turf is less ordinary: a kidney-shaped accumulation of burnt material, the characteristic signature of a fulacht fia.

A fulacht fia is a type of prehistoric cooking or processing site found in considerable numbers across Ireland, typically consisting of a trough, a hearth, and a mound of fire-cracked stones. The stones would be heated and dropped into a water-filled trough to bring the water to a boil; the cracked and discarded stones gradually built up into the distinctive horseshoe or kidney-shaped mound that survives today. The example at Garranes follows this form closely, with an eastern-facing opening measuring roughly 1.2 metres across. What makes this particular site quietly compelling is that it does not stand alone. A second fulacht fia lies approximately 25 metres to the east, suggesting that this stretch of hillside above the Glantrasna River saw repeated or sustained use, perhaps across generations, by people who found something reliably useful about this south-facing slope and its proximity to the valley below.