What makes it worth pausing over is not its size, which is modest, roughly ninety centimetres by a little over a metre, but what has been worked into its surface. Prehistoric rock art of this kind is easily missed, and on this particular stone the carvings are described as very faint, distributed across a triangular face that the elements have had a long time to weather.

The motifs belong to a tradition of prehistoric mark-making found widely across Atlantic Europe, concentrated in Ireland largely in the south-west and north-west. The vocabulary is abstract and repetitive: cupmarks, which are small circular hollows pecked into the rock surface, and cup-and-ring marks, where one or more concentric grooves surround a central cup. On this boulder, the principal carvings occupy a central area not much larger than a human hand, comprising a single cupmark and a cup-and-one-ring, each picked to a depth of just a few millimetres. Across the broader surface, approximately twenty-six smaller pickmarks of varying sizes are scattered, and a creep of vegetation along the northern edge may be concealing further marks beneath. A second rock art site lies roughly eight metres to the north-east. The Derreeny stone was recorded in the 1996 archaeological survey of the Iveragh Peninsula compiled by A. O'Sullivan and J. Sheehan, and later resurveyed in greater detail.

The boulder sits at around 168 metres above sea level, on a low rise with views across the Ballaghbeama Gap to the north-west and down into the Kealduff River valley to the south. That positioning, open and elevated relative to its immediate surroundings, is a feature noted at many Irish rock art sites, where landscape setting seems to have mattered to whoever chose the stone. Whether the carvings functioned as boundary markers, ritual aids, or something else entirely, nobody now knows. The motifs offer no text to read, only a set of deliberate marks made by someone who understood their meaning and assumed others would too.