It measures about eight metres in length, with an opening some three metres wide, and it belongs to a class of monument that has turned up in the thousands across Ireland: the fulacht fia. The name, roughly translated, refers to an ancient outdoor cooking place, and the characteristic horseshoe shape comes from the gradual accumulation of fire-cracked stone discarded after repeated heating. The working principle was simple enough; stones were heated in a fire, then dropped into a water-filled trough to bring it to boiling point, which could then be used for cooking meat or, as some researchers have argued, for other purposes including textile preparation or even bathing.

The proximity to a stream is entirely typical. Water was the essential ingredient, and fulachtaí fia are almost always found close to a reliable source of it. Most examples in Ireland date from the Bronze Age, roughly 1500 to 500 BC, though some sites have yielded dates extending into the early medieval period. The mound at Ballynatona is the physical residue of that repeated process, burnt stone piled up over many uses until it formed the low, rounded shape that survives today. Across County Cork and the wider Munster region, these monuments occur in remarkable density, suggesting that whatever activity took place at them was a regular and probably communal part of daily or seasonal life rather than something occasional or ceremonial.