Situated on a rocky island on the River Suir, Cahir Castle is one of the largest and best preserved castles in Ireland. It was originally built in the 13th Century on the site on an earlier Irish cathair. The full form of the placename in Irish is Cathair Dhun Iascaigh, which could be translated as the "stone fort of the fortress of the fishery".

The castle was granted to the Butler Family, Earls of Ormond, in the late 14th century. It was enlarged during the 15th to 17th century time period, but was abandoned by the family and fell into ruin in the late 18th century. It has since been restored after being acquired by the state, and has appeared in the 1981 film Excalibur.