A cashel is a ringfort built from stone rather than earth and timber, and this one, a subcircular enclosure measuring roughly 22.6 metres from north to south, has been almost entirely absorbed into the working landscape around it. The drystone wall that once defined its perimeter now lies beneath a later field wall built along the same line, the modern boundary and the ancient one occupying the same ground.

Cashels of this type were typically constructed during the early medieval period, broadly between the fifth and twelfth centuries, and served as enclosed farmsteads for individual farming families. The ringfort, in its various forms of earthen rath, stone cashel, or lakeside crannog, was the defining settlement type of early medieval Ireland, and thousands survive in varying states of preservation across the country. This particular example in Garrynagry is among the less legible, described in the published Archaeological Inventory of County Galway as poorly preserved, its entrance opening to the north. The fact that a field wall now runs directly over it is not unusual; farmers across centuries have found it practical to incorporate old stone structures into new ones, and in doing so have inadvertently preserved the footprint, if not the form.