This rectangular tower, measuring 8 metres north to south and 7 metres east to west, features a small projection on its southern wall that once housed a garderobe chute; a medieval necessity that discharged waste directly into the sea below. Though time hasn’t been kind to the structure, with the southeast corner having collapsed and much of the ground floor now filled with rubble, the castle still reveals its clever defensive design through a doorway in the centre of its eastern wall and an internal passage leading to mural stairs that spiral from the northeast to southeast corners, providing access to all upper floors.

The second floor boasts a remarkable stone roof constructed from three pointed arches, separated from each other and the side walls by overlapping stone slabs, though several have fallen over the centuries. Beyond the tower, the remains of a bawn, or defensive courtyard wall, stretch approximately 30 metres east to west and 20 metres north to south. This outer defence included a D-shaped tower at its northwest corner and various buildings at the southeast corner that connected directly to the main tower house. To the east, traces of a smaller enclosure can still be seen, complete with the ruins of a building containing a bread oven; essential for feeding the castle’s garrison.

As the stronghold of the O’Driscoll clan, who controlled much of the maritime trade along this stretch of coast, Doonanore Castle played its final military role in 1602 when it surrendered to Crown forces after a brief siege during the Nine Years’ War. This marked the end of the O’Driscolls’ centuries-long dominance of these waters and the beginning of the castle’s slow decline into the atmospheric ruin that greets visitors today.