This is a fulacht fia, a type of prehistoric cooking or processing site found in great numbers across Ireland, typically identified by a horseshoe-shaped mound of fire-cracked stone and charcoal. The stones were heated in a fire and then dropped into a water-filled trough to bring it to the boil, a method that left behind dense accumulations of shattered, heat-blackened material. At Castlemary, that spread of burnt debris is now grass-covered, absorbed into the working landscape of a field.

What gives the site an additional layer of interest is its proximity to a megalithic structure roughly 130 metres to the south-west. Megalithic monuments, a broad category encompassing portal tombs, wedge tombs, stone circles, and standing stones, were frequently constructed during the Neolithic and Bronze Age periods, and fulachta fia are similarly associated with Bronze Age activity, roughly 1500 to 500 BC. Whether the two sites at Castlemary were in use at the same time, or whether one preceded the other by centuries, is not something the surviving evidence settles. But the pairing is a quiet reminder that these landscapes were not empty between their monuments; people were cooking, gathering, and going about daily work in the spaces between.