It is not a dramatic monument ringed by interpretation boards; it is simply there, a large fractured stone with the Atlantic visible to the north between Drung Hill and Droum, and the Coomasaharn mountains rising to the west. What makes it quietly remarkable is the density and variety of what has been pecked and grooved into its surface across three distinct decorated faces.

The vocabulary of motifs belongs to the tradition of prehistoric Atlantic rock art, a broad corpus of abstract carving found across Ireland, Britain, and Atlantic Europe, generally dated to the Neolithic and early Bronze Age periods. Cup-and-ring marks, the most recognisable form, consist of a small circular depression, the cup, enclosed by one or more concentric rings carved into the rock surface. At Ballynakilly, the main concentration sits close to ground level on the north-east side of the north-west-facing aspect. Here, two cross-and-ring motifs, each a simple incised cross enclosed within a circular ring, are connected to one another by a linear groove, and a second groove links them onward to a cup-and-two-ring motif, creating a kind of visual chain across the stone. A penannular ring, meaning a ring left deliberately open at one point rather than closed, sits just three centimetres to the north of that grouping. The flat top of the boulder carries a further pair of cup-and-two-ring motifs aligned north to south, while the south-east-facing side bears two long curvilinear grooves sweeping across its lower surface. Some of the linear grooves cutting across the rings appear relatively fresh and may be modern additions, a complication that is not unusual on sites that have sat in agricultural land for centuries.

The boulder is accessible within a working pasture field, so the motifs close to ground level require crouching to examine properly. The weathering means the carvings are legible rather than vivid; a low, raking light, such as that on an overcast day or in the slanted sun of early morning or late afternoon, tends to bring out shallow relief carving far more effectively than direct overhead light.