The castle at Annaghdown emerged from the Archbishops of Tuam’s efforts to suppress the local bishopric, with the last bishop appointed here in 1421 likely responsible for constructing the present structure. By 1574, the property had passed into the hands of Nicholas Lynch, part of one of Galway’s prominent merchant families.

The almost square tower measures 11 metres in length and 10.3 metres in width, rising five storeys high and remaining in remarkably fair condition. Its defensive features are still clearly visible: a pointed arch doorway in the southeast wall leads into a lobby watched over by a murder hole, whilst the ground floor contains a guardroom to the south and a passage north to the intramural stairs. The tower retains its stone vault between the second and third floors, and architectural details include simple rectangular window slits, the remains of two light windows, and evidence of a fireplace on the first floor’s southwest gable. At the top, corbels that once supported angled bartizans can be seen on three corners, whilst chimney stacks crown both gables and slop stones survive on most walls.

Traces of the original bawn wall, standing less than 2 metres high and 0.85 metres thick, extend southward from both the eastern and western corners of the tower. The eastern section preserves both a slit window and a gun loop, indicating the castle’s continued defensive adaptations over time. Near the base of the northwest wall, the exit chute for the garderobe serves as a reminder of the practical considerations of medieval castle life, whilst the combination of defensive and domestic features throughout the structure illustrates how this tower house served both as a fortification and a residence for its successive owners.