The example at Drumsheel, in County Mayo, quietly breaks that rule. Sitting on the south-eastern summit of a hill, now given over to pasture, it forms a roughly square enclosure, measuring 28 metres north to south and 27 metres east to west. A cashel, as a stone-walled ringfort is known, typically used a drystone wall to define a farmstead or defended homestead, and here the wall survives to a width of about one and a half metres and a height of just under a metre. That is modest, but enough to read clearly in the landscape.

On the eastern side there is a gap some seven metres wide, identified as a possible original entrance, though a later stone field fence now runs across it, layering one era of land use over another in the way that Irish fields tend to do. Inside the enclosure, cultivation ridges are still visible in the ground surface, the corrugated pattern left by lazy-bed farming, where soil was mounded into parallel ridges to improve drainage and grow crops, most commonly potatoes. Whether those ridges date to the early medieval period when the cashel was likely in use, or to a much later reoccupation of a convenient enclosed space, is not recorded. The square plan itself is unusual enough to suggest this site repays a second look from anyone passing through the Ballinrobe district with an interest in the less tidy edges of Irish archaeological classification.