It measures roughly 16.5 metres long, 13.5 metres wide, and stands about 0.9 metres high, with an opening six metres across facing east. To a passing eye it might read as a natural rise in the ground, or an old field boundary that lost its purpose. In fact it is a fulacht fia, one of the most common yet least understood monument types in the Irish landscape.

A fulacht fia is essentially the debris left behind by repeated episodes of water heating, typically achieved by dropping fire-cracked stones into a water-filled trough. As the stones shattered with use, they were raked out and piled up, creating over time the distinctive crescent or horseshoe shape that defines the type. These sites are found in their thousands across Ireland, dating mainly to the Bronze Age, though some were in use into the early medieval period. Their precise function remains debated; cooking is the most widely accepted explanation, but brewing, hide-working, and bathing have all been seriously proposed. The eastward-facing opening at Newcastle is a commonly observed feature of the type, and may reflect a practical preference for morning light, proximity to a water source now altered or gone, or simply the lie of the land as it was understood by the people who first chose the spot.