It is not much to look at from a distance, but its shape and position tell a story that stretches back thousands of years. This is a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland and Britain, typically Bronze Age in date. The standard interpretation is that water was brought or channelled into a timber-lined trough, and stones were heated in a nearby fire before being dropped into the water to bring it to the boil. The discarded, fire-cracked stones accumulated over repeated use into the characteristic horseshoe-shaped mound that survives today.

The mound at Knockawillin measures roughly twelve metres along its northwest to southeast axis and just over ten metres across the other way, rising to about sixty centimetres at its highest point. The opening of the horseshoe, two metres wide, faces northwest, which is where the working area and trough would originally have been. The proximity to the stream, a little over a dozen metres to the north, is entirely typical. Fulachtaí fia are almost invariably found close to a water source, and the stream here would have supplied the essential ingredient for whatever was being prepared, whether that was food, hot water for other domestic purposes, or something else entirely. Debates about their precise function have never been fully settled, and some researchers have proposed uses ranging from textile processing to bathing.