Built by the Mac Fhirbhisigh family, who served as hereditary historians to the O’Dubhda clan, this four-storey fortification reflects the turbulent period when Gaelic lords and Norman-Irish families alike constructed defensive residences throughout the countryside. The castle’s rectangular form, measuring roughly 10 by 8 metres, follows the typical design of tower houses from this era; thick limestone walls pierced by narrow windows and topped with distinctive Irish crow-stepped gables.

The Mac Fhirbhisigh family, whose anglicised name became Forbes or MacFirbis, were renowned scholars who maintained one of Ireland’s most important scribal schools at nearby Lackan. From this castle and its surrounding lands, they produced genealogical manuscripts and historical chronicles that remain invaluable sources for understanding medieval Irish society. The family’s scholarly tradition continued here until the Cromwellian conquest of the 1650s, when their lands were confiscated and redistributed to English settlers, marking the end of nearly four centuries of Mac Fhirbhisigh influence in the region.

Today, the castle stands as a lonely sentinel overlooking Killala Bay, its walls still largely intact despite centuries of Atlantic storms. The structure retains many original features, including a spiral staircase built into the thickness of the wall, murder holes above the entrance, and the remnants of a bawn wall that once enclosed a courtyard. While the wooden floors have long since rotted away, visitors can still trace the outline of the great hall on the first floor and imagine the castle in its heyday, when it served as both a defensive stronghold and a centre of Gaelic learning.