Built from roughly coursed rubble with a distinctive base batter, the rectangular tower features two angle towers projecting from its eastern face. Though the main doorway in the recessed eastern wall has been destroyed, the structure remains an impressive example of medieval defensive architecture. A possible bawn wall extends from the southwestern angle of the tower, whilst evidence suggests the remainder of this defensive enclosure may lie hidden beneath ground level.

The castle's immediate surroundings reveal intriguing features that hint at its former extent and importance. To the southwest lies what appears to be an old quarry, likely the source of building materials for the tower's construction. A natural spring well sits within a possible enclosure to the east, though dense vegetation now prevents thorough examination of this area. Earthworks visible here may represent the levelled remains of the bawn or perhaps buildings that once stood within its protective walls. A 1985 survey by FAS documented that the tower house sits atop an earthen mound surrounded by a ditch, with a low earthen bank visible along its northern perimeter; these features appear to be the remnants of the castle's original bawn defences.

Archaeological evidence suggests Drumnamahane Castle was once part of a more elaborate defensive complex than what survives today. The combination of natural rock outcrop, constructed earthworks, and stone fortifications would have created a formidable stronghold controlling this stretch of poorly drained pasture. Whilst time and agricultural activity have obscured many of the site's original features, the tower itself continues to dominate the landscape, offering visitors a glimpse into the region's turbulent medieval past.