Known both as Knockainy Castle and the White Castle, the four-storey limestone structure was reportedly built around 1500 by Matthew O’Grady, who served as steward to the Earl of Desmond. Local tradition suggests O’Grady constructed the castle whilst the Earl was abroad, and it remained in use until roughly 1700 when it began its gradual decline into ruin. By 1840, rather than housing nobility, the castle had become home to a weaver.

The tower house showcases typical defensive features of its era, including a pointed barrel vault over the third floor, a fortified entrance on the eastern side complete with murder hole above, and walls measuring seven feet thick. The entrance doorway retains evidence of its security measures; a yett hole in the jamb, recesses for a bar, and a spud stone for the door. Inside, the castle was divided into multiple chambers across its floors, with the lowest level being vaulted and measuring 22 feet by 13½ feet. The spiral staircase in the north-east angle provided access between floors, whilst narrow window slits and ogee-headed windows illuminated the various rooms. Several chambers featured wall cupboards for storage, and at least one contained a garderobe chamber with remnants of a ledge for a wooden seat.

Today, the castle stands partially covered in ivy with its roof and wall-walk missing, though much of its structure remains intact enough to reveal its original layout. The building appears on historical maps including the 1654-7 Down Survey where it’s marked as ‘White Castle’, and the 1837 Ordnance Survey map where it’s labelled ‘Knockainy Castle’. Located 300 yards east of the castle are the remains of the Earl of Desmond’s ‘Court’, situated south of the river. The castle has been protected under a preservation order since 1937, ensuring this piece of medieval Irish architecture continues to tell its story to future generations.