The road does not cut straight through; it curves, following the arc of a structure that was already old when the first Ordnance Survey cartographers passed through, which suggests that whoever laid out that road knew, or at least sensed, that something significant occupied the rise at Barnacahoge.

The site sits at the break of slope on a high ridge, commanding views in every direction, which is precisely the kind of position favoured by the builders of raths, the earthen ringforts that served as enclosed farmsteads across early medieval Ireland, typically from around the fifth to the twelfth century. What survives at Barnacahoge is a roughly D-shaped area, approximately thirty metres north to south and just over twenty-one metres east to west, with its flat eastern side formed by the road itself, which has truncated the original arc. The western half of the enclosure is defined by a scarp, a stepped earthen bank cut into the natural slope, dropping roughly one metre to a narrow terrace or berm before dropping again by a further 1.2 metres. These two successive drops, though modest in scale, would have given the interior a commanding and defensible aspect. The 1838 and 1930 Ordnance Survey maps both record the enclosure as roughly circular with a diameter of between twenty-five and thirty metres, confirming that the shape visible today is largely the result of road-building eating into the eastern arc rather than any more recent disturbance.

The interior is level, and within it are two earthwork features that reward careful looking. In the northern half, a grassed-over depression, about 1.5 metres wide and half a metre deep, runs northward for over four metres before turning westward and widening to almost 2.5 metres as it approaches the scarp. Its function is unclear, though such depressions within ringforts can sometimes represent the remains of drainage channels, structural slots, or collapsed features. A few metres to the south of this lies a slight circular hollow roughly three metres in diameter, faint enough to be easily missed in long summer grass but more legible when the vegetation is low.