The boulder is a glacial erratic, meaning it was transported far from its original geological context by ice and deposited as the glaciers retreated, leaving it stranded and conspicuous on the hillside. What makes this particular erratic unusual is not its size, roughly three metres by three metres and up to 1.75 metres high on its southern and western sides, but the fact that a prehistoric hand chose its upper face as a surface worth marking.

The carvings belong to a tradition known as cup-and-ring art, a form of prehistoric rock art found across Atlantic Europe and Ireland, in which circular depressions, called cupmarks, are sometimes surrounded by one or more incised concentric rings. At Derreeny, the motifs are concentrated towards the northern end of the boulder's upper surface. One cup-and-ring mark has a central cupmark roughly six centimetres in diameter enclosed by two faint rings, and in oblique light, the kind that rakes across a surface at a low angle and picks out shallow carving, traces of two or more additional partially enclosing rings become visible to the west. South of this sits a larger cupmark, around seven centimetres across, with its own faint enclosing ring. Adding to the interest of the site, directly south of the boulder there is a hemispherical enclosure, possibly the remains of a small hut, whose straight northern side is partially formed by the boulder's own southern face. The stone, in other words, may have served not just as a canvas but as a structural element in a much later, or perhaps contemporary, domestic arrangement. The site was identified and recorded by Aoibheann Lambe in March 2023.