A cashel is a ringfort built from stone rather than earth, the drystone wall serving as both boundary and defence for whoever farmed and lived within. What makes Ballyryan quietly interesting is not the cashel alone but the cluster of structures around and inside it, each pointing to a settlement that was, at some point, carefully organised across this modest patch of ground.

The cashel is roughly subcircular in plan, measuring 28 metres north to south and 26 metres east to west. Where the drystone wall has not been swallowed by vegetation, sections of outer facing survive, particularly to the north, north-east, and east-south-east, where the wall still stands to around a metre in height externally. Inside the southern portion of the enclosure, a curved stony bank with internal facing may represent a house site, the kind of secondary structure commonly tucked against a cashel's inner wall for shelter. More unusual is the souterrain in the northern interior, an underground stone-lined passage or chamber of the sort built throughout early medieval Ireland, probably for storage and possibly for refuge. A large glacial erratic, a boulder deposited here by ice during the last glacial period and entirely unworked by human hands, sits in the south-western quadrant, a reminder that the people who built here simply incorporated what the landscape had already left behind. That this was not an isolated farmstead is suggested by a second cashel and associated hut site located roughly 98 metres to the west, close enough to imply a community rather than a single household. The site was already being mapped by the time the Ordnance Survey revised its six-inch sheets in 1915, indicating it was visible and recognisable well into the modern period.