This rectangular three-storey tower house, with its distinctive projecting towers at the western and southern corners, tells the story of one of Ireland’s most resilient Catholic noble families. The Barnwalls, who became the Barons Trimlestown in 1461 under Edward IV, managed to hold onto their estates through centuries of religious and political upheaval, though the castle itself has been a ruin since the 1830s.

The castle’s original medieval core dates from the fifteenth century, featuring thick walls with embrasures and a mural staircase that winds up from the ground floor entrance on the southeast wall. The building underwent significant alterations in the eighteenth century, including the addition of a northeastern wing with an impressive bay window, though this too now lies in ruins. Inside, the original layout reveals a ground floor with five embrasures along the northwest wall, one later converted into a fireplace, whilst the upper floors were accessed via both mural and newel staircases. The second floor, positioned above a vault, once featured large windows and fireplaces that may have been added during later renovations.

The Barnwalls’ tenure at Tremblestown reflects the complex religious politics of Irish history. Despite being Catholic, they retained their core estates even as the castle served as a Confederate Catholic stronghold during the 1640s before surrendering to Cromwellian forces in 1647. The family’s fortunes shifted dramatically in the eighteenth century when Robert, the twelfth Lord Trimlestown, championed Catholic causes whilst his own sons converted to Protestantism. By the end of that century, the Barnwalls had abandoned the castle, eventually severing their connection with Tremblestown entirely, leaving behind these evocative ruins set within what may be a medieval field system, complete with the remains of an old church, mills, and bridge that once made this a thriving estate.