Measuring roughly seven metres east to west and twelve metres along its straight eastern side, and rising to just three-quarters of a metre in height, it is not the kind of feature that announces itself. What it contains, though, is distinctive: heat-shattered stones and soil darkened by charcoal, the calling card of a fulacht fia.

Fulachtaí fia are among the most common prehistoric monuments in Ireland, found in their thousands across the island. The basic idea behind them was practical rather than ceremonial: stones were heated in a fire and then dropped into a water-filled trough, bringing it rapidly to a boil. The cracked, discarded stones accumulated over time into the characteristic horseshoe or D-shaped mounds we see today, with charcoal-stained soil filling the gaps. What exactly these sites were used for remains debated, with cooking, textile processing, and bathing all proposed as possibilities. What is clear is that this mound at Rossnashunsoge was not a solitary operation. Two further fulachtaí fia lie within roughly a hundred metres, one approximately forty metres to the north and another around eighty metres to the south, suggesting that this particular patch of Cork countryside saw repeated, possibly sustained, prehistoric activity around the same water source. Adding another layer of depth, a pre-bog wall abuts the mound on its eastern side. Pre-bog walls are field boundaries that predate the growth of blanket bog over a landscape, meaning this wall was already ancient when the bog began to form, and its presence alongside the mound hints at an organised, inhabited landscape stretching back well before anyone thought to write anything down.