What lies beneath the pasture is the levelled remains of a fulacht fia, an ancient outdoor cooking site of a type found scattered across the Irish landscape in their thousands. The site sits on a barely discernible platform measuring roughly 28 metres east to west, and within that platform is an irregular spread of burnt material covering approximately 11 metres north to south and 9 metres east to west. The platform itself is old enough to have been marked on the First Edition of the Ordnance Survey maps, where it appears as a hachured enclosure, a cartographic shorthand for a raised or bounded feature on the ground.

Fulachtaí fia, to use the Irish plural, are among the most common prehistoric monuments in Ireland. They typically consist of a horseshoe-shaped mound of fire-cracked stones, the debris from a process of heating water in a trough by dropping hot stones into it, used for cooking, bathing, or textile processing, depending on which theory you favour. The Ballythomas example was already in a levelled state when it came to scholarly attention. A researcher named Bowman noted it in 1934, recording it as a fulacht fiadh on land belonging to a P. O'Callaghan. By that point the mound had clearly been reduced, either by agricultural activity or the slow work of time, leaving the spread of burnt material as the main surviving evidence. A separate enclosure lies just over 113 metres to the south-west, hinting that this small corner of North Cork was an area of some activity in the prehistoric period.