The castle consists of a polygonal shell keep with an enclosing curtain wall, a corner tower and a gate tower. The shell keep is the earliest structure, dating from the 12th century. Shell keeps are common in England, but rare in Ireland. Inside the curtain wall is a two-story military barracks, which dates from the first half of the 18th century. As this site is managed by the OPW, school tour visits are permitted free of charge provided certain conditions are met.