This modest medieval tower house sits beside an old mountain pass called Barnaderg, placing it strategically within a network of similar fortifications; Shankill Castle lies a kilometre to the south-southeast, Ballycorus Castle 1.2 kilometres southwest, and Laughanstown Castle 1.4 kilometres north. The castle's proximity to Rathmichael's round tower, church and graveyard just 600 metres away suggests it played a role in the parish's medieval defensive landscape, though curiously it doesn't appear on the 17th-century Down Survey map of the area.

The castle itself is a simple oblong structure measuring roughly 10.25 metres by 7.6 metres, with walls over a metre thick at the base. Built directly on bedrock that still protrudes through the floors in places, the building rises to about 9.7 metres at its highest point, where remnants of a small stair turret remain. The interior originally contained three floors connected by stone staircases; eleven steps led to the first floor, with another flight directly above reaching the second, and a short circular stairway in the turret provided access to the roof. A slight projection on the north side housed garderobes on the upper floors, whilst chimney flues on the eastern wall served fireplaces on multiple levels. Evidence of brickwork and plaster indicates the castle was inhabited well into modern times, with various windows and doorways modified over the centuries.

What makes Puck's Castle particularly interesting is the survival of its bawn, or fortified enclosure. Grass-covered earthworks still trace the outline of this defensive yard, which appears to have extended considerably from the castle walls before turning at right angles to form a large rectangular space, possibly subdivided into sections. The foundations of an additional building adjoin the castle's east side, and what may be a partially circular well can be found within the outer yard. First mapped by John Rocque in 1762 as "Puck Castle in Ruines", the structure was carefully documented by E.R. Dix in 1897, by which time a thoughtful landowner named Mr. Orpen had installed a flat roof to protect the interior from the elements, helping preserve this atmospheric remnant of medieval Rathmichael.