Cahir castle (pronounced "care") is in County Tipperary.
It's one of Ireland's largest and best preserved castles (13-19th century).

The tour of this castle is especially interesting--our guide explained what it was like for a castle to be under siege and showed us some of the castles defense systems.

The square structure above the arch is called a "machicolation." Castle defenders would pour boiling liquids or throw rocks through the opening onto the heads of attackers trying to get through the gate.