Known locally as Caisleán na Circe (Hen’s Castle), this fortress was built around 1235 by Feidhlim, king of Connacht, to replace an earlier castle that had been burnt down just two years prior. The structure, now designated as National Monument 245, originally belonged to the O’Connor clan before eventually passing into the hands of the O’Flahertys, reflecting the shifting political landscape of medieval Galway.

The castle itself is a compact but formidable structure, consisting of a rectangular keep measuring approximately 12.2 by 11.6 metres internally, with small square towers at each corner and walls that taper outward at the base for added stability. Entry to the fortress was cleverly designed for defence; visitors would have crossed what was likely a removable wooden bridge to reach a sturdy doorway set within a forebuilding at the south tower. From there, an internal stairway led through the tower midway along the southwestern wall to reach the first-floor hall, which occupied the entire upper level. The basement, now filled with rubble but once accessible via spiral stairs in the eastern tower, shows evidence of wooden floor joists above it that supported the hall.

While the roof, parapets and wall-walks have long since disappeared, the castle bears clear signs of renovation during the 15th and 16th centuries, suggesting it remained an active stronghold well beyond its initial construction. Small details like the latrine chute visible on the exterior of the northeastern wall offer glimpses into daily life within these stone walls. Archaeological evidence confirms historical accounts of the castle’s continued occupation through the late medieval period, making it a valuable window into centuries of Irish castle building and clan warfare along the shores of Lough Corrib.