It is, in fact, the remains of a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland, typically Bronze Age in origin. The fulacht fia usually consisted of a trough filled with water, which was heated by dropping fire-cracked stones into it; the discarded burnt stones accumulated over time into the distinctive mound shape that survives today.

The Derryroe example is a reasonably substantial specimen. The mound measures eleven metres in length and nine metres in width, rising only half a metre above the surrounding ground, with an opening of three and a half metres facing north-west, giving it the characteristic horseshoe or kidney outline. A large pile of stones now sits atop the mound, which may reflect later interference or simple accumulation over the centuries. The site was recorded by Hartnett in 1939, placing it within a long tradition of scholarly attention to such monuments in Cork, a county that contains one of the densest concentrations of fulachta fiadh in Ireland.