The castle once stood on what was known as Castle Island or Lough Coura, a small island surrounded by wet, marshy land that would have provided natural defence against would-be attackers. Today, only fragments remain of what archaeological surveys suggest was once a circular tower with walls measuring approximately 1.2 metres thick and an internal diameter of around 4 metres.

The surviving structure offers few clues to its original appearance, with just a piece of wall fragment and scattered rubble marking where this defensive stronghold once stood. South of the tower ruins, loosely piled rubble spread across the ground surface hints at what may have been a bawn wall; a defensive courtyard wall typical of Irish tower houses and castles from the medieval period. These protective walls would have enclosed livestock and provided an outer line of defence for the castle’s inhabitants.

Historical records from the 19th and early 20th centuries, including accounts by Cooke in 1875 and O’Flanagan in 1933, document the site when more of the structure may have been visible. While time and the elements have reduced Castle Island to little more than stone fragments, the site remains an intriguing piece of Offaly’s medieval landscape, offering a glimpse into how natural geography was incorporated into defensive architecture in medieval Ireland.