The more substantial of the two is a cashel, a type of ringfort defined not by an earthen bank but by a drystone wall, built without mortar from locally gathered stone. This one stretches roughly 36 metres across, though its enclosing wall has largely collapsed inward, leaving a low, irregular scatter of rubble that only becomes legible as a deliberate structure when you trace its curve. The best-preserved stretch survives at the south-east.

Cashels of this kind were typically built and occupied during the early medieval period in Ireland, roughly from the fifth to the twelfth centuries, and served as enclosed farmsteads for individual family groups. The choice of drystone construction at Manuslynn rather than earthwork is characteristic of areas where surface stone is plentiful, as it certainly is across the limestone karst of north Galway. Immediately to the north-east of the cashel wall, an elongated mound of grass-covered stone, about seven metres long, two and a half metres wide, and less than a metre high, sits in a way that suggests some relationship to the enclosure, though its precise function remains unclear. Whether it is a collapsed outbuilding, a field clearance heap, or something else is not recorded. Thirty metres to the south-east, a separate ringfort occupies the same rough terrain, and the proximity of the two sites raises the possibility that they formed part of the same agricultural or social landscape, perhaps used by related or successive communities.