The boulder is modest in size, roughly 1.46 metres along its longest axis and only 0.4 metres high, the kind of thing you could walk past without a second glance. Look closely, though, and the surface reveals a quiet complexity: fourteen single cupmarks, which are small, deliberately pecked depressions in the rock, alongside a cup-and-ring motif and three cup-and-two-ring motifs, where a central cupmark is surrounded by one or two concentric carved rings. The motifs are faint and spread evenly across the sub-oval decorated face, sitting to one side of a natural linear striation that runs north to south along the stone. The view from the boulder opens southward, down the length of the Kealduff river valley.

Rock art of this kind is generally associated with the Bronze Age, roughly 2500 to 500 BC, though its precise meaning and function remain genuinely unresolved. The cup-and-ring form appears across Atlantic Europe, from Galicia to Argyll, and Ireland has a considerable concentration of examples, particularly in Munster and Ulster. What made certain boulders and outcrops worthy of this kind of attention is not fully understood. At Derreeny, the decorated stone sits within what was once a managed landscape: an old field system still survives here, and a drystone field boundary runs just a few metres to the west. The boulder is not isolated but part of a cluster; another carved stone lies roughly 18 metres to the north, and the surrounding area is scattered with earthfast boulders and loose rock of varying sizes, making it difficult to know at a glance which stones carry marks and which do not.

The motifs at Derreeny are described as faint, which is worth bearing in mind for anyone making the effort to locate the site. Low, raking light, particularly in the morning or evening when shadows settle into the shallow depressions, tends to make carved surfaces far more legible than they are under flat midday light. The boulder sits at around 151 metres above sea level on open mountain pasture, a working landscape that has changed relatively little in its basic character since the field boundaries were first laid out.