Its strategic importance meant it changed hands frequently throughout its history; granted to the Fitzgeralds in 1285, they held it until 1535 when the Earl of Ossory took possession. The turbulent Confederate Wars saw it change ownership four times before Oliver Cromwell finally captured it in 1649. Rather remarkably, the castle continued its military role well into modern times, serving as a garrison throughout the 17th century, with barracks added before 1746, and even functioning as a Garda station until 1987.

Today’s well-preserved remains reveal a sophisticated medieval fortress built around a subrectangular ward. At the northwest angle stands a polygonal shell-keep, originally surrounded by a moat as excavations in 1996 revealed. Its first-floor entrance and internal features include a large vaulted chamber measuring 17.4m by 5.2m, complete with loops later adapted for artillery, a garderobe passage, and window embrasures. The southeast gatehouse displays classic defensive architecture with two D-shaped towers connected by a vaulted passage, complete with portcullis groove and murder-hole. The curtain walls, standing about 5.5 metres high along the south and west sides, feature both gun loops and blocked arrow loops at wall-walk level.

The southwest corner houses an impressive circular tower, roughly 10.7 metres in diameter and 11 metres high, containing three floors with a later-inserted vault over the ground floor. Its defensive features include three embrasures at ground level, arrow-loop embrasures partially obscured by wicker-centred vaulting at first-floor level, and a second-floor garderobe. Archaeological excavations in 1997 uncovered additional structures including a building beside the keep, a cistern in the hall, and evidence of an earlier rectangular corner tower at the northeast angle that was replaced by another tower in the 15th or 16th century, though this later structure no longer survives.