It is roughly D-shaped, about sixteen metres from east to west and eight metres across, rising less than a metre above the surrounding ground. What fills it is stranger than the shape: heat-shattered stones packed into charcoal-rich soil, the accumulated debris of an activity carried out here perhaps three or four thousand years ago.

This is a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland, particularly in low-lying or waterlogged ground. The basic method involved heating stones in a fire, then dropping them into a water-filled trough to bring it rapidly to the boil. The cracked, spent stones were piled to the side after each use, and over time these discards built up into the horseshoe or D-shaped mounds that survive today. The wet pasture setting at Magheragillerneeve is entirely typical: fulachtaí fia almost always appear near a water source, and the boggy, undulating ground here would have supplied that readily. The southern edge of the mound is cut by a field ditch two metres wide, which slices through the site where it meets a natural east-west rise in the land. That a later boundary should bisect the mound so cleanly is a reminder of how thoroughly these features have been absorbed into the ordinary working landscape over the centuries. A second fulacht fia survives roughly 225 metres to the north-east, suggesting that this stretch of ground saw repeated or prolonged use across prehistoric times.