Though marked as ‘Convent (in Ruins)’ on 19th and early 20th century Ordnance Survey maps, the surviving structures tell a different story. Historical records from 1574 list a castle at ‘Carnan’ owned by one John Oge fitz John fitz Ed, and the architectural evidence supports this identification. The main feature is a roughly oval enclosure crowning the hill summit, measuring approximately 50 metres east to west and 32 metres north to south. Its most striking element is an almost square turret of 16th-century construction at the southeast corner, rising two storeys high with rectangular windows on each level and traces of spiral stairs tucked into the northeast corner.

The defensive layout suggests this was indeed a fortified residence rather than a religious house. The inner enclosure is defined by mortared stone walls and banks, with a substantial defensive ditch cutting across the western approach to the hilltop. Inside, the uneven ground reveals traces of internal structures including north-south running walls, what might have been a rectangular house, and a large quarry pit. A second, larger earthen enclosure rings the base of the hill, measuring 125 metres by 105 metres, complete with banks, ditches, and two entrances; one to the north with a causeway across the fosse, and another to the east. Radial banks connect the inner and outer defences, creating a sophisticated defensive system that archaeological surveys suggest may represent an Anglo-Norman ringwork castle.

The confusion over its identity likely stems from post-Reformation occupation. Local tradition, recorded in 1838, referred to the turret as ‘the nunnery tower’, suggesting that nuns may have occupied the castle at some point after its military significance waned, though no documentary evidence exists for a formal convent at this location. Today, these substantial ruins offer a glimpse into the layers of Irish history, from medieval fortification to possible religious refuge, all set within the pastoral landscape of County Galway.