The castle’s turbulent history reflects the political upheavals of its time; the O’Loughlins frequently clashed with English authorities, receiving multiple pardons in the late 16th century that saw the castle regranted to them. Following a rebellion in 1632-33, the property was officially disposed of to George Martyn, Mayor of Galway, though it remained within the O’Loughlin family through the strategic marriage of Turlough O’Loughlin to Martyn’s daughter Alice. Their descendants, who adopted the Martyn name, continued to live in the area until recent times, whilst the castle itself fell into ruin before 1837.

The rectangular tower house measures 10 metres north to south and 7 metres east to west, rising three storeys and incorporating the northwest wall of an enclosing bawn. Built from uncoursed limestone rubble masonry with surviving traces of external render, the structure features finely cut quoins and architectural details that date it to the first half of the 16th century. Entry is through a pointed arch doorway on the eastern wall, defended by a machicolation above, leading to a ground floor with two parallel vaulted chambers. The building’s defensive features include a porter’s chamber, a secure bolt-hole chamber with corbelled ceiling that could be locked from outside, and an intricate system of intramural stairs that begin straight before spiralling through the southeast corner to reach the upper floors.

The first floor contains a single large chamber spanning 9.1 by 4.5 metres, complete with garderobe shaft, multiple mullioned windows, and a centrally placed fireplace flanked by an aumbry and chimney flue. External corbels at the southwest angle once supported a corner machicolation, adding to the tower’s defensive capabilities. The second floor features a mantled fireplace believed to date from the 17th century, along with a double-mullioned window providing natural light. After lying in ruins for over a century, the castle underwent renovation in the mid-1990s, bringing new life to this remarkable example of Irish tower house architecture that once commanded the Barony of Gragans.