A fulacht fia, sometimes also called a burnt mound, is one of the most common prehistoric monument types in Ireland, yet for all their frequency, exactly what they were used for remains an open question. Cooking, bathing, textile processing, and brewing have all been proposed. What makes the Ballythomas example quietly remarkable is what survives beneath that modest scatter of scorched stone.

Excavation revealed two separate troughs, both cut into the ground and both preserving organic material that rarely endures. The larger is oval, roughly one and a half metres by one and a third metres and thirty-five centimetres deep, with a layer of wicker lining its base, along with traces of what may have been moss. A ring of stakeholes around the trough's edge suggests some kind of wooden structure once stood over or around it. A fragment of one of those stakes was radiocarbon dated, placing it between 1120 and 858 cal BC, in the Later Bronze Age. The second trough is smaller and sub-rectangular, about one and a quarter metres by just under a metre and twenty centimetres deep. Several lengths of unworked timber lay across its base, interpreted either as a deliberately laid floor or as material that slumped inward after the structure above it decayed. This trough returned an earlier radiocarbon date, between 1727 and 1528 cal BC, suggesting the site saw activity across a considerable span of time, or that the two features belong to entirely separate episodes of use. Adding another layer of interest, a horizontal mill was also identified nearby, pointing to a wider pattern of early activity in this part of Cork.