Built sometime in the medieval period, this castle served as a defensive stronghold controlling access along important waterways in the region. The name itself, meaning ‘Castle of the Hen’ in Irish, hints at local folklore that has long since been woven into the fabric of the site’s history, though the exact origins of this peculiar moniker remain unclear.

The castle’s ruins reveal typical medieval Irish tower house construction, with thick limestone walls designed to withstand both the Atlantic weather and potential sieges. Archaeological evidence suggests the site was occupied by various Gaelic clans throughout its active years, particularly the O’Malleys, who dominated Mayo’s coastal territories during the late medieval period. The structure likely featured multiple floors connected by spiral staircases built into the walls, with the ground floor serving as storage whilst the upper levels provided living quarters for the castle’s inhabitants.

Today, the remnants of Caislen-na-Circe offer visitors a glimpse into Mayo’s turbulent past, when control of waterways and coastal access points meant the difference between prosperity and subjugation. The castle’s island location, whilst now peaceful and relatively isolated, once made it nearly impregnable; attackers would have faced the challenge of crossing water whilst under fire from the castle’s defenders. Though time and weather have reduced much of the structure to rubble, enough remains to appreciate the engineering skills of medieval Irish builders and the strategic importance this lonely outpost once held.