This rectangular stone structure, measuring 7.4 metres from north to south and 10.7 metres from east to west, was built from roughly coursed granite boulders with walls over a metre thick. While most of the castle has been reduced to its foundation courses, the northern wall still reaches an impressive height of around three metres, giving visitors a sense of the building’s original scale.

The castle’s construction appears remarkably straightforward; there’s no surviving evidence of an entrance, arrow loops, or a vaulted ceiling, suggesting this was likely a simple tower house rather than an elaborate fortification. The thick granite walls would have provided both defence and insulation for its inhabitants, typical of the practical architecture favoured by minor landowners during the medieval period.

Today, what remains of Ballytarsna Castle offers a glimpse into the lives of those who once controlled this part of rural Carlow. The site, documented in the Archaeological Inventory of County Carlow in 1993, continues to be studied by researchers piecing together the story of Ireland’s numerous small castles and tower houses that once dotted the countryside.