Built in the 13th century by the Fitzmaurice family, this stronghold commanded sweeping views of the river, with the tide reaching within 70 metres of its walls. The castle’s name has sparked debate amongst historians; whilst it appears as ‘Beaulieu’ in the 1633 text Pacata Hibernia, and Richard Cox suggested in 1687 that it derived from ‘Beal-a-bo’, the scholar O’Donovan argued in 1841 that it comes from ‘béal’, meaning mouth or bay, referring to its strategic position at the river’s edge.

The castle witnessed one of the more intriguing murders of the Tudor conquest period. In August 1600, Maurice Stack, a close associate of the English commander Lord Carew, met his doom within these walls. Historical accounts differ on who orchestrated the conspiracy; Pacata Hibernia portrays Honora O’Brien, wife of Thomas Fitzmaurice, 18th Lord of Kerry, as the principal agent who lured Stack to his death, whilst the Annals of the Four Masters suggests she was merely a pawn manipulated by her husband. This murder came after Thomas Fitzmaurice attempted to surrender to Carew during the wars of the 1600s, only to have his peace offering rejected, turning him into a lifelong enemy of the English Crown. Ironically, Lord Kerry himself had already destroyed the castle’s fortifications in 1581 to prevent English forces from using them.

Today, only the foundations remain of what was once an impressive tower house. According to Westropp’s 1909 survey, the original structure had two floors beneath a vault, another vaulted storey above, and a roofed upper room. The visible ruins form a rectangular enclosure measuring 68 metres north to south and 62 metres east to west, surrounded by earthen banks that still rise up to 1.8 metres in places. Traces of what appears to be a defensive fosse and outer bank can be spotted at the northeast and southeast corners, hinting at the castle’s once formidable defences. The castle remained in Fitzmaurice hands until 1783, when it passed to Richard Hare, marking the end of five centuries of family ownership.