At roughly thirteen metres long, nine and a half metres wide, and no more than twenty centimetres high at its tallest point, it would be easy to walk past without a second glance. But beneath that unassuming hump lies the signature of a fulacht fia, a type of prehistoric cooking site found widely across Ireland, typically consisting of a trough for boiling water, a hearth, and the accumulated debris of fire-cracked stone that was heated and dropped into water to bring it to the boil.

The site at Derrylough came to wider attention not through deliberate excavation but through the more prosaic business of land reclamation. Workers improving the ground encountered quantities of burnt stone at and around the mound, the characteristic material that marks these sites and gives them their distinctive profile. That fractured, fire-reddened stone, discarded after each use, slowly accumulated into the low horseshoe-shaped or oval mounds that remain today. The surrounding landscape, with its extensive areas of raised bog stretching to the west and north-west, is typical of the environment in which fulachtaí fia are often found; boggy, waterlogged ground would have supplied the reliable water source these sites required, and the peat has in many cases helped preserve what little survives.