They are fulachtai fiadh, a type of prehistoric cooking place found in enormous numbers across Ireland, typically consisting of a mound of fire-cracked stone beside a water trough. The principle was straightforward: heat stones in a fire, drop them into a water-filled pit, and bring the water to a boil. The mounds that survive today are essentially the accumulated debris of that process, the discarded, shattered stones piling up over repeated use.

At Carrignafeela, roughly 150 metres north of the River Lee, the low-lying ground between the ridges would have provided both the marshy conditions these sites seem to favour and a reliable water source nearby. A survey of the Lee Valley area carried out by Michael Connolly in 1996 and 1997 recorded all three mounds and measured the largest in some detail. It runs 15 metres north to south and 11 metres east to west, rising to an average height of around 0.70 metres. The trough area, the central pit where water was heated, measures 5 metres by 4 metres and sits 0.40 metres below the crest of the surrounding mound, with a one-metre-wide entrance opening to the east. The material piled across the whole cluster is shattered red sandstone, the local geology leaving its mark even on the prehistoric record.

The setting itself is worth pausing on. The combination of steep ridges, a river corridor, and waterlogged ground between them describes a landscape that has changed relatively little in character since the Bronze Age, even if the specifics have shifted. The sites are grassed and reed-covered now, which means they read more as gentle undulations in a wet field than as obvious monuments. Knowing what to look for makes the difference.