It is about twelve metres long, eight metres wide, and less than a metre high, and it is composed almost entirely of burnt, shattered stone. That description alone sets it apart from the ordinary bumps and hollows of a grazed field, because what lies underfoot is the accumulated debris of prehistoric cooking, possibly repeated over generations.

This is a fulacht fia, a type of ancient cooking site found in considerable numbers across Ireland, particularly in low-lying, waterlogged ground. The typical arrangement involved a trough, often timber-lined or stone-lined, filled with water, into which stones were heated in a nearby fire and then dropped to bring the water to a boil. The spent, cracked stones were discarded to the side, building up over time into the characteristic horseshoe-shaped or kidney-shaped mound that survives today. At Newcastle, a stream rises to the south-east of the site, which fits the pattern well; fulachta fiadh are almost always found close to a reliable water source. Most examples date to the Bronze Age, broadly between 1500 and 500 BC, though the tradition appears to have persisted in some areas beyond that period. The mound here, at roughly 0.65 metres in height, is modest but intact enough to read as a coherent monument rather than a vague earthwork.