Furmina Castle, Inis Oírr, Co. Galway

This two-storey rectangular keep, measuring 13.2 metres long by 7.6 metres wide, dates likely to the 14th century despite its early architectural design. The castle remained in active use well into the 16th century; records from 1574 note it was held by one Domynick Lynch, before reportedly meeting its demise at the hands of Cromwell's forces in 1652.

The castle's original entrance sits on the first floor of the northeast wall, flanked by beam holes that once supported external wooden stairs. This doorway opened into a great hall that occupied the entire first floor, though its vaulted ceiling has largely collapsed over the centuries. Below, the ground floor basement contains three vaulted chambers, accessible only through an opening in the central chamber's roof. Intramural stairs built into the southwest wall's thickness once provided access to the wall walks and parapets above.

Despite centuries of weathering, several architectural features remain remarkably intact. The tall merlons pierced with arrow slits still crown parts of the walls, whilst a corbel from a bartizan survives at the north corner. The southwest wall features a particularly fine single-light window with a trefoil head, and decorated projecting corbels can be spotted on the external faces of both the northeast and southeast walls. The structure has been a National Monument since the 1930s, ensuring its preservation as one of the Aran Islands' most significant medieval ruins.