This is a cashel, a type of ringfort built from dry-stone walling rather than earthen banks and ditches, and the example at Ballymurphy is small but remarkably coherent. Measuring roughly 19.5 metres east to west and 18.6 metres north to south, it sits on a slight rise within a gently south-facing plateau, the kind of modest elevation that would have offered its original occupants good drainage and a clear view of the surrounding land without advertising itself unnecessarily to the wider countryside.

The cashel is defined by a double-faced stone wall, meaning the structure has a distinct outer and inner face with rubble fill between them. The outer face, built from horizontally laid stones, can be traced almost all the way around the circuit, and it stands between 0.8 and 1.2 metres high on the exterior side. The entrance, only about a metre wide and easy to miss, is positioned at the south-south-east, placed just to the east of a single upright stone set into the outer wall-face. Against the inner wall-face, a spread of stones has accumulated or been banked, suggesting the wall's original bulk was considerably greater than what survives today. The structure was already being recorded cartographically by the late nineteenth century, appearing on the 1897 Ordnance Survey 25-inch plan and again on the 1920 edition of the 6-inch map. It sits within a large multiperiod field system, indicating that the agricultural organisation of this ground stretches across many centuries and several phases of use. A second cashel of similar character lies roughly 50 metres to the west-south-west, raising the possibility that these enclosures functioned in some relationship to one another, though what that relationship was remains a matter of inference rather than record.