Nenagh Castle was built by Theobald Walter (the first of the Butlers of Ormond) around 1200. To this day the cylindrical keep adorns the town and like most keeps, it formed part of the perimeter of the fortress. The walls have now almost disappeared, but fragments remain. Built from limestone Nenagh Castle measures fifty-five feet in external diameter at the base and rises to a height of one hundred feet. As this site is managed by the OPW, guided school tour visits are facilitated free of charge provided certain conditions are met.