A fulacht fia, the term used for these ancient burnt-mound sites, typically consists of the accumulated debris from a simple but effective method of water-heating: stones were fired in a hearth, then dropped into a water-filled trough until the contents boiled. Over repeated use, the shattered, heat-cracked stones were raked aside, building up the horseshoe-shaped mounds that survive across the Irish countryside in their thousands. At Barnalyra, the mound measures roughly 9.5 metres from north-west to south-east and 5.5 metres across, rising to a maximum height of about 0.8 metres at its southern end. A shallow indentation on the western face, closest to the stream, is thought to indicate where the trough once sat.

What makes Barnalyra quietly notable is not any single feature but the concentration of activity along this one small valley. Three further fulachtaí fia lie within 55 metres of this mound, strung along the same stream corridor, suggesting that this particular watercourse drew people back repeatedly, or perhaps simultaneously, over an extended period. The mound itself has not escaped interference entirely; a farm track has cut into its eastern side, and a noticeable hollow on the north-east edge hints at further disturbance. A dense growth of gorse now obscures much of the surface, making the full outline difficult to read from ground level, though the charcoal-rich soil visible at the edges speaks plainly enough to the heat and industry that once took place here.