The boulder is modest in scale, barely thirty centimetres at its highest point, with a roughly diamond-shaped decorated surface. What it carries is prehistoric rock art: cupmarks, cup-and-ring marks, and a double cup-and-ring, all pecked and ground into the stone by hand, probably during the Bronze Age.

Cupmarks are exactly what the name suggests, small circular depressions hollowed into rock, typically a few centimetres across and only a few millimetres deep. Cup-and-ring marks add one or more concentric carved rings around a central cup. Their meaning remains genuinely uncertain; they appear across Atlantic Europe and occur in Ireland with particular frequency in upland and marginal landscapes. At Derreeny, the motifs number around twenty cupmarks of varying sizes, nine cup-and-ring combinations including one with only a partial ring, and a more elaborate double cup-and-ring measuring nearly nineteen centimetres across. The carvings are concentrated toward the eastern and northern areas of the boulder's surface, and described as very faint, worn down by weather and time into the grain of the stone. A roughly L-shaped feature crosses the south-western half of the decorated surface and may also be man-made, though this is not certain.

The boulder sits at around 168 metres above sea level on a south-facing slope, looking out over the Kealduff River valley to the south and, to the north-west, towards the Ballaghbeama Gap, a dramatic mountain pass cutting through the Iveragh Peninsula. Whether that orientation was deliberate is impossible to say now, but it is hard to stand at the stone and not notice that the view it faces is a significant one.