The boulder has a slightly hogback profile, rising to about 0.7 metres on its south-east side and dropping to just 0.2 metres on the north-west, and measures roughly 1.8 metres along its north-east to south-west axis. What makes it quietly arresting is not its size but what was done to its surface: eight cup marks, each between four and eight centimetres in diameter, run along the high central ridge, with a further two or possibly three cups on the south-east face.

Cup marks are among the most ancient and most puzzling forms of prehistoric rock art found across Ireland and Britain. They are simple hemispherical depressions, ground or pecked into stone surfaces, and while they appear throughout the prehistoric record, their purpose remains genuinely unclear. Ritual use, territorial marking, astronomical alignment, and purely symbolic expression have all been proposed, and none has been conclusively established. The Downshill example fits a recognisable pattern in that the cups are arranged along the most prominent part of the stone, the central ridge, where they would have caught the light and been most visible to anyone approaching across the slope. The choice of an earthfast boulder, one that is fixed in the ground rather than free-standing, is also typical; such stones were not placed by human hands but were already features of the landscape, selected and then worked upon.