The boulder measures roughly 2.25 metres in length and stands about 0.9 metres tall, though its true width is difficult to assess because part of it remains buried. What makes it quietly puzzling is that the broad face now standing upright and looking westward was most likely, at some point in the distant past, the horizontal upper surface of a flat boulder, lying open to the sky rather than facing out across a valley.

Scattered across that surface, concentrated at opposite corners, are six cup marks. Cup marks are among the simplest and most enduring forms of prehistoric rock art, shallow circular depressions pecked into stone by hand, found across Ireland and Britain from the Neolithic and Bronze Age periods. Nobody has settled on a definitive explanation for what they meant to the people who made them, though theories range from ritual or astronomical significance to territorial marking. Here at Killeagh, the surface itself is far from smooth, with natural undulations and hollows already interrupting the rock, and the cup marks sit within that uneven terrain, chosen or arranged with some intention that has long since passed out of memory. The boulder's position on a ridge with wide views to the west may or may not have mattered to whoever worked the stone, but it is the kind of detail that lingers once you know to look for it.