It measures roughly nine metres north to south and eight metres east to west, standing just 0.4 metres high. What gives it away is what lies beneath: nearly a metre of burnt and fire-cracked stone, revealed where the mound has been cut through on its eastern side by a stream. This is a fulacht fia, one of thousands of Bronze Age cooking sites scattered across the Irish landscape, and one of the most numerous yet least remarked-upon monument types in the country.

A fulacht fia typically consists of a horseshoe-shaped mound of shattered stone beside a trough and a water source. The working theory, supported by experimental archaeology, is that stones were heated in a fire and then dropped into a water-filled trough, bringing it to a boil rapidly and repeatedly. The shattered, heat-spent stones were then raked aside, building up over time into the distinctive mound that survives today. The site at Gurranes fits this pattern closely: the stream on its eastern side would have provided a ready water supply, and the mound itself is composed of that characteristic burnt material, the accumulated debris of repeated use. These sites date broadly to the Bronze Age, though some continued in use into the early medieval period, and their precise social function, whether cooking, bathing, textile processing, or some combination, remains a matter of ongoing discussion among archaeologists.