This late 15th-century tower house rises four storeys from its rectangular base, measuring roughly 7 by 5.5 metres, with walls nearly two metres thick. Built from a mix of locally sourced limestone, sandstone, granite and conglomerate, the castle features the characteristic base batter common to Irish tower houses of this period. The original entrance on the north wall still shows evidence of its defensive drawbar sockets, whilst remnants of a bawn wall with an angle tower can be traced about 1.6 metres from the main structure.

The castle’s interior reveals the typical defensive architecture of its time. A stone staircase built into the western wall’s thickness originally led from the entrance to the first floor, which featured wooden flooring supported by corbels. Above this sits a stone vaulted ceiling, with a ladder opening providing access to the second floor. From here, stone stairs lead to the upper levels, which also had wooden floors, and ultimately to the battlements. The defensive features include machicolations projecting from three sides; the south, west and north; notably absent from the eastern seaward side. Most windows are simple rectangular openings, though two round-headed slit windows survive in the upper floors, and a garderobe chute is built into the southern wall’s western end.

Whilst local tradition firmly links the castle to the legendary pirate queen Grace O’Malley, or Granuaile, who lived from around 1530 to 1603, the architectural evidence suggests the structure predates her by several decades. The castle was more likely built by one of her O’Malley ancestors, who controlled this strategic coastal position. Today, Kildavnet Castle is protected as National Monument No. 458 under State ownership, with a preservation order in place since 1949, ensuring this remarkable piece of Ireland’s maritime heritage remains intact for future generations to explore.