Built by the O’Haras, this medieval fortification originally rose higher than its current two storeys, though time and the elements have claimed most of its eastern and southern walls. The tower’s sturdy construction of uncoursed limestone blocks set in lime mortar, complete with a distinctive base batter, has helped the remaining structure endure centuries of Irish weather, even as ivy gradually colonises its outer faces.

The castle’s interior reveals the practical defensive architecture typical of Irish tower houses. At ground level, blocked window embrasures pierce the north and west walls, whilst the original entrance has been lost to decay. An entresol level above contains another blocked window and the remnants of sophisticated features including a garderobe chamber tucked into the southwest corner, accessed by a now partially destroyed mural staircase built directly into the south wall. The first floor, reached through a lintelled doorway via another mural stairs, would have been the main living space, lit by windows on three sides and equipped with its own garderobe facility; a practical arrangement that provided both comfort and security to its medieval inhabitants.

The landscape surrounding the tower tells its own story of human activity. A build up of fallen masonry has created a scarped edge about a metre high along the eastern wall, whilst beyond this lies a sunken area that appears to be the result of limestone quarrying, possibly for the castle’s own construction or later building projects. A natural spring in this depression adds to the site’s strategic advantages, providing a ready water source that would have been invaluable during times of siege. First documented by antiquarians like Francis Grose in 1791 and later by historians including McParlan and O’Rorke, Moymlough Castle stands as a testament to the defensive needs and architectural skills of medieval Sligo’s ruling families.