McDermott's Castle
McDermott's Castle, also known as Castle McDermott or Cloonalis Castle in some local references, stands on a small rocky island in Lough Key, County Roscommon, one of the most picturesque and historically resonant sites in the Irish midlands. The ruin rises from the waters of this island-studded lake with a quiet authority that immediately communicates its long and layered past. It is most commonly identified as the stronghold of the MacDermot clan, a powerful Gaelic Irish family who held sway over the kingdom of Moylurg for centuries, and the island setting made it both defensible and dramatically striking. Visiting it today requires a boat trip across the lake, which only adds to the sense of stepping into a different era entirely.
The MacDermots — whose name translates roughly as "son of Dermot" — were among the most significant royal families of medieval Connacht, and their island fortress on Lough Key served as the seat of their power for much of the medieval period. The castle itself dates in its present ruined form to around the 15th or 16th century, though the island had likely been fortified and inhabited for centuries before that. The MacDermots are mentioned extensively in the Annals of Lough Key, a chronicle compiled at or near this very location, making the site not just a political stronghold but also a center of Gaelic literary and religious culture. Monks and scribes associated with the nearby Boyle Abbey and the monastic traditions of the region contributed to records that help modern historians understand medieval Ireland in considerable detail.
One of the most enduring stories connected to this site is the tragic legend of Una MacDermot and the poet Tomás Láidir Costello, said to be one of the sources of inspiration behind the famous Irish song "Una Bhan" (Fair Una). According to the tale, Una, daughter of the MacDermot chieftain, fell in love with Costello, but her father disapproved of the match and separated the lovers. Una reportedly died of a broken heart and was buried on an island in the lake, and it is said that when Costello was finally allowed to visit her grave, he lay down beside it and never rose again. Whether historically accurate or not, the story has woven itself deeply into the cultural fabric of the region, and the ruins of the castle carry that romantic, melancholic atmosphere with them still.
Physically, the castle is a striking ruin of grey limestone walls rising directly from the rocky shoreline of its small island. Substantial sections of the walls remain standing, with enough height to give a clear impression of the structure's original scale and formidable presence. Vegetation has crept into the stonework over centuries, and the island is heavily wooded, so that approaching by boat the castle appears to emerge from a tangle of green, its pale stone contrasting with the surrounding trees and water. The sound environment is dominated by birdsong and the lapping of the lake, with the occasional creak of reeds in a breeze — a profound quiet that makes the site feel genuinely remote even though it is not far from civilization.
Lough Key itself is one of the finest lakes in Connacht, dotted with about thirty islands and fringed by mature woodland managed as part of Lough Key Forest and Activity Park, which surrounds much of the lake's shoreline. The park, managed by Coillte and situated near Boyle, offers walking trails, a treehouse experience, a bog garden, and boat hire facilities that allow visitors to get out onto the water and view the various islands and their ruins. Boyle town, a few kilometers to the west, provides services including accommodation, restaurants, and access to Boyle Abbey, a magnificent Cistercian ruin that is one of the best-preserved medieval abbeys in Ireland. The wider area of County Roscommon is not heavily touristed, which gives it a pleasantly uncrowded quality even in summer.
To visit Castle McDermott properly — meaning to get out onto the water and see it up close — visitors should make use of the boat hire available at Lough Key Forest Park during the warmer months. The park is well signposted from the N4 road near Boyle and has ample parking. Summer is the best time to visit for boat access and for exploring the park's many amenities, though spring and autumn offer a quieter experience and often dramatic light over the lake. The island itself may not always be accessible to land on, so it is worth checking locally about current access conditions before planning to step ashore. Regardless, even a circuit of the lake by boat gives a rewarding and memorable encounter with this historic ruin.
A fascinating and somewhat overlooked aspect of the site is its connection to the annalistic tradition of early Ireland. The Annals of Lough Key, also known as the Annals of Boyle, are a chronicle running from the early Christian period to the 13th century, and they record events across Ireland with a particular focus on Connacht. The proximity of this monastic and scholarly activity to a powerful secular Gaelic lordship like that of the MacDermots illustrates the intertwined nature of church, learning, and political power in medieval Ireland. The castle and its island thus represent not just military architecture but a whole world of Gaelic civilization that was largely dismantled in the 16th and 17th centuries during the Tudor and Cromwellian conquests. Standing on the lakeshore or drifting past by boat, it is not difficult to feel the weight of that lost world pressing gently against the present.