Built sometime during the 15th or 16th century, this five-storey square tower house in County Limerick has witnessed centuries of changing ownership and architectural transformation. The castle first appears in historical records in 1586, when Brian Buí O'Brien of Castlegarde was noted as one of the county's loyal gentlemen during a period of rebellion. Following the Desmond Rebellion in 1588, the Crown confiscated a plowland of Castlegarde and granted it to Sir George Bourchier as part of his Lough Gur estate. By the 17th century, the property had passed to Henry Bourchier, 5th Earl of Bath, and notably escaped confiscation during the Cromwellian land settlements as it was already in English hands.

The castle's most significant transformation occurred in the 1820s under Waller O'Grady, youngest son of the 1st Viscount Guillamore. Following his marriage in 1823, O'Grady commissioned architects James and George Richard Pain to modernise the medieval tower whilst preserving its historic character. The Pain brothers, known for their Gothic Revival work across Ireland, added a castellated wing to the structure, restored the old bawn walls with battlements, and created a new gateway with an accompanying lodge. The renovations, which cost approximately £5,000 by 1829, carefully maintained the tower house's external appearance whilst making the interior rooms suitable for comfortable living. It was likely during this romantic revival period that the castle acquired its dubious connection to Brian Boru, with his carved head appearing above the entrance door, though no genuine historical link exists.

Today, the complex presents a fascinating blend of authentic medieval architecture and 19th-century romantic additions. The original tower house retains its rubble limestone walls with roughly dressed quoins and a distinctive battered base, whilst the attached four-bay country house showcases the Pain brothers' Gothic Revival sensibilities with its crenellated battlements, pointed arch doorways, and decorative hoodmouldings. The site is enclosed by limestone bawn walls punctuated by carved towers, and curious visitors might spot the three carved limestone statues depicting classical deities; Bacchus, Mars, and Athena entwined with a fish; on the north-east elevation. Despite John O'Donovan's 1840 observation that he could find no historical references to the castle, modern research has revealed its complex history of ownership, from the O'Briens through English proprietors to its 19th-century reinvention as a gentleman's Gothic residence.