This is a fulacht fia, a type of site found in considerable numbers across Ireland and generally interpreted as an ancient cooking place, though brewing, textile processing, and bathing have all been proposed as alternative or additional uses. The typical arrangement involved heating stones in a fire, dropping them into a water-filled trough until the water boiled, and then using that heat to cook meat or serve some other purpose. The discarded, fire-cracked stones accumulated over time into the characteristic horseshoe-shaped or oval mound that survives today.

The mound at Coolbaun measures roughly ten metres north to south and twelve metres east to west, rising to about 0.7 metres in height, which is modest but consistent with many examples of the type. What makes the location quietly notable is the proximity of a second fulacht fia sitting approximately twenty metres to the south-southwest. The pairing is not unique in Irish archaeology, and clusters of these sites are sometimes found sharing a water source, but it does suggest repeated or sustained use of this particular stretch of ground beside the stream. The marshy, waterlogged conditions that might seem to make the spot inconvenient were likely part of the attraction, since a ready and reliable water supply was essential to the whole process.