That positioning is no accident. A rath, as ringforts of this type are generally known, is an early medieval enclosure typically built to define a farmstead and signal status; placing one on a ridge with a steep fall on one side gave its inhabitants both a clear view and a natural defensive advantage without the labour of engineering it themselves.

The enclosure at Rathduff measures roughly 38 metres east to west and just over 36 metres north to south, making it a reasonably substantial example. Its defining feature is an earthen bank, about 3.7 metres wide and standing up to 1.5 metres high on the southern side, with small stones along the top and occasional larger ones breaking the surface. A gap of around 1.2 metres in the eastern bank, flanked by a large stone on its southern edge and a second stone set slightly to the north, is likely the original entrance, though it is poorly defined now. The bank has also eroded in several other places, at the north, northwest, and southwest. Inside, the ground is level and grassy. What draws the eye, though, is a circular depression in the southeast quadrant, about 7 metres across and 0.6 metres deep, covered over with grass. Its significance is not clear; such features within ringfort interiors have been interpreted variously as the remains of a sunken structure, a collapsed souterrain (an underground stone-lined passage associated with early medieval settlement), or simply as the result of later disturbance. This one remains an open question.

The rath is set in pasture and ringed by hazel, holly, hawthorn, and blackthorn, the kind of scrubby boundary planting that has come to be almost characteristic of these sites across Ireland, whether by long tradition or simply because livestock have never grazed right up to the bank. The tree line gives the interior a noticeably enclosed quality that the modest height of the bank alone would not produce.