The cairn at Coomshanna is not large: roughly three and a half metres across and just over a metre tall, subcircular in plan, composed of a loose jumble of stone with a scattering of quartz worked through it. That quartz is a small but telling detail. Across prehistoric Ireland, quartz appears repeatedly at burial and ritual monuments, and its presence here, however modest in quantity, hints that this structure was probably more than a simple boundary marker or field clearance.

The cairn sits on the Iveragh Peninsula in County Kerry, a landscape that was surveyed and documented by archaeologists A. O'Sullivan and J. Sheehan in their 1996 study of the peninsula's ancient remains. The mountain itself, Beenmore, commands an unusually wide field of view: Dingle Bay opens out to the north, while the valleys of the Behy and Ferta rivers run away to the east and west. It is the kind of position that people in many different periods chose deliberately, whether for burial, for ceremony, or simply to mark that a summit had meaning. Without excavation, the cairn's precise date and purpose remain open questions, but the combination of prominent placement, deliberate construction, and that hint of quartz suggests it belongs to a tradition of upland monument-building that stretches back into prehistory across much of Atlantic Ireland.