It is a rath, the most common type of ringfort in Ireland, typically a farmstead enclosed by one or more earthen banks, and home to a family of some local standing during the early medieval period. What makes this particular example quietly interesting is the engineering thought that went into levelling its interior: the builders raised the ground inside to counteract the natural slope of the hillside, so that the northern half of the floor tilts gently southward while the southern half sits flat. The result is a roughly level living space hidden inside what looks, from the outside, like an unassuming bump in a field.

The fort is roughly circular, with a diameter of about 19.5 metres, and its defining feature is an earthen scarp, essentially a steep-sided bank, running between three and four and a half metres wide and standing one and a half to two metres high. There is no visible fosse, the term for the outer ditch that typically accompanies such banks, though one may once have existed and silted over across the centuries. On the western side, an irregular ramp about three metres wide is thought to mark where the original entrance once stood. The livestock that graze the surrounding pasture have left their own modest mark, wearing a slight step into the scarp partway up its sides. A second enclosure of similar character sits roughly 250 metres to the east, suggesting this corner of Ballynacree may once have supported more than one such enclosed settlement.

The interior is clear of overgrowth, which means the earthworks read well at ground level, the raised platform and the curve of the scarp both visible without having to fight through scrub. The western ramp, where the entrance is thought to have been, gives the clearest sense of how the structure was originally approached.