A cairn, at its most basic, is a human-made mound of stones, often associated with burial, boundary-marking, or ritual activity, and this one at An Inse Mhór is small even by those unassuming standards: roughly three and three-quarter metres long, two and a half metres wide, and only half a metre high, oriented along a north-south axis.

The cairn came to wider attention through an archaeological assessment carried out in 2010 by Quinn and Carroll of Tobar Archaeological Services, commissioned in connection with a proposed wind farm at the nearby townland of Doonens. That context is worth noting: it is often infrastructural development, rather than dedicated research excavation, that draws professional attention to sites like this one. The assessment placed this cairn in relation to a group of other cairns in the immediate area, suggesting that whatever purpose these stone accumulations once served, it was not entirely solitary. Whether they represent a prehistoric funerary landscape, territorial markers, or something else altogether, the documentary record does not say.