This substantial tower house served as the principal residence of the O’Sullivan Mores, with Owen O’Sullivan and his second wife, Sily MacCarthy Riabhach, reportedly building an adjoining manor house after Owen’s inauguration as O’Sullivan More in 1580. The castle remained in O’Sullivan hands until 1656, when it was confiscated and acquired by Sir William Petty, despite repeated attempts by the family to petition for its return.

The ivy-clad tower house rises to 18.3 metres at its northern wall, though much of the structure has collapsed; only the north wall stands to its full height whilst the south, east and west walls survive merely to the upper levels of the ground floor. Built from roughly coursed limestone blocks and rubble, the rectangular castle measures 12 by 10.8 metres with walls averaging 2.6 metres thick at the base. A small turret, likely serving as an oubliette dungeon, is attached to the south side. The building originally comprised four storeys, each containing a main chamber with additional mural passages and smaller chambers in the upper levels. The first floor was roofed with a now-collapsed vault, and communication between floors was likely via a spiral stair in the southeast angle, though this section has largely fallen away.

Today, visitors can still observe many architectural details that speak to the castle’s defensive capabilities and daily life within its walls. The ground floor entrance, accessed through the remnants of a small bawn, leads to a vaulted lobby with a mural stair ascending to the first floor. Throughout the building, embrasures for windows and loops show evidence of shutters secured by drawbars, whilst wall cupboards and garderobe chambers indicate the domestic arrangements of its inhabitants. Curiously, the base of the castle now features the concrete remains of several stages of a crazy golf course, a rather unexpected modern addition to this medieval stronghold.