The Rock of Dunamase, 6km east of Portlaoise, is an arresting sight: a craggy limestone outcrop rising 45m out of the flat plains. It offered early settlers a superb natural defensive position looking out across the surrounding countryside. The ruins here are those of a castle built in the 12th century. You'll need some imagination to envisage the site as it was before it was destroyed by Cromwell's henchmen in 1650, but the views from the summit are breathtaking.
The rock was first fortified in the Bronze Age. Over the centuries that followed, successive waves of Viking, Norman, Irish and English invaders fought over its occupation and control. The castle was extensively remodelled in the 15th century, and fell into decline until its 17th-century destruction.
On a clear day, you can see Timahoe round tower to the south, the Slieve Blooms to the west and the Wicklow Mountains to the east.