That near-invisibility is itself the point. Beneath the grass lies a spread of burnt material, the remains of a fulacht fia, a type of prehistoric cooking site found in their thousands across Ireland. The name, loosely translated as "cooking place of the deer" or sometimes "burnt mound", describes a broadly consistent technology: a trough filled with water, heated by dropping fire-cracked stones into it until the water boiled, then used to cook meat or, as some researchers now suggest, for brewing, hide-working, or bathing. The stone, shattered by repeated heating and cooling, was raked aside into a characteristic horseshoe-shaped mound. Over millennia, that mound can sink back into the ground until almost nothing remains above the surface.

The site at Ballymurphy appears to be at that advanced stage of disappearance. The burnt material spread through the pasture is the only surviving indicator of what was once here. A well recorded on the Ordnance Survey six-inch map of 1940 stood roughly twenty metres to the north, though no visible trace of it now remains at the surface either. The proximity of the stream valley is entirely typical; fulachtaí fia are almost always found close to a reliable water source, since the entire process depended on it. Bronze Age in date for the most part, though some examples span into the Iron Age, these sites represent one of the most common categories of field monument in Munster, and Cork in particular has a dense concentration of them.