The castle overlooks a stream called 'The Brook' to the west, which marks the boundary with Doon Demesne, and sits 320 metres north of Doon Cross Roads. This location was particularly significant in medieval times as it controlled the intersection of two major routes: the 'Bealagh Leathcoill', or Pass through the half wood, which connected Ferbane to Athlone along what is now the N62, and the 'Togher', a medieval routeway that traversed Mac Coghlan's country from east to west. Parts of the Togher survive today as the Pilgrims Road between Clonmacnoise monastery and Ballycumber village, with the R444 road partially following its original line.

The castle itself reveals a complex building history through its architectural features. The rectangular structure measures 8.6 metres north to south by 12.6 metres east to west, with walls 1.8 metres thick constructed from random rubble sandstone. Evidence suggests the castle underwent substantial rebuilding in the 16th century; the north and east walls display dressed cut stone alternating quoins typical of that period, whilst the northwest and southwest angles retain earlier, roughly shaped undressed quoins. The presence of a prominent base batter only on the south and west walls, along with a large buttress against the western wall's southern end, indicates that the newer walls were built onto the remains of an earlier structure. A rather remarkable feature is a horizontal sheela na gig carved in relief on the southeast angle at first floor level, one of the more unusual architectural elements to survive from medieval Ireland.

The interior layout demonstrates sophisticated defensive planning typical of tower houses. Entry was through a pointed doorway on the eastern wall, originally protected by an iron yett (gate) with evidence of its draw chain hole still visible. This led to a small vaulted lobby area that appears to have been inserted into the earlier castle, as its vault line cuts across an existing window embrasure. Beyond the lobby, a mural staircase in the southeast angle provided access to upper floors, complete with a murder hole positioned directly above the entrance for defensive purposes. The main ground floor chamber measures 5.45 metres by 3.95 metres and shows evidence of multiple building phases, including windows from both the 13th and 16th centuries. The first floor contained similar dimensions but featured more refined elements including an ogee headed window and access to a garderobe chamber in the northwest angle, demonstrating the combination of defensive architecture with residential comfort that characterised these later medieval strongholds.