This three-storey stronghold, now partially covered in ivy, served as the seat of the Crimeen branch of the MacCarthy Riabhach family. The castle remained inhabited well into the 19th century, with various modifications made over the centuries to accommodate changing needs; notably, the original door and window openings were altered to accommodate wooden frames.

The tower’s defensive architecture reveals careful planning typical of medieval Irish fortifications. Entry is gained through a central door in the western wall at ground level, which opens into a vaulted lobby. From here, a spiral staircase tucked into the northwest corner provides access to all three floors and eventually leads to the wall walk at the top of the tower. The internal layout divides the space efficiently, with smaller chambers positioned above the lobby area whilst the main rooms occupy the eastern section of the structure. Strategic gun loops pierce the western wall at first-floor level, offering defensive coverage, and a bartizan, though now concealed by ivy, projects from the southwest corner of the tower’s summit.

Despite its isolated setting in this marshy terrain, Derrylemlary Castle stands as a well-preserved example of a late medieval Irish tower house, its continued occupation into relatively modern times ensuring its structural integrity. The castle’s adaptation over the centuries, from medieval fortress to more comfortable dwelling, tells the story of how these defensive structures evolved to meet the changing circumstances of their inhabitants whilst maintaining their essential character as symbols of local power and authority.