The castle’s most distinctive surviving feature is its southeast wall, part of a barrel-vaulted building constructed from granite boulders. This substantial wall runs northwest to southeast and showcases the defensive architecture typical of Irish tower houses, with large embrasures on both the ground floor and in the loft space beneath the vault.

Today, visitors will find the castle in a state of considerable ruin. Large chunks of fallen masonry and accumulated debris obscure much of the original ground plan, making it difficult to fully appreciate the building’s original layout and scale. Despite its ruined condition, the remaining stonework demonstrates the solid construction techniques employed by medieval builders, who used locally sourced granite boulders to create a structure meant to withstand both time and conflict.

The castle has been documented by various surveys over the years, including the Ordnance Survey Letters of 1939 and the Irish Tourist Association Survey of 1945. These historical records, along with the more recent Archaeological Inventory of County Carlow published in 1993, help piece together the story of this once-formidable stronghold. While Coppenagh Castle may lack the grandeur of better-preserved Irish castles, it remains an authentic example of the hundreds of tower houses that once dotted the Irish countryside, serving as both homes and fortresses for the Anglo-Norman and Gaelic families who shaped medieval Ireland.