Cahir's castle enjoys a river-island site with massive walls, towers and keep, mullioned windows, original fireplaces and a dungeon. Founded by Conor O'Brien in 1142, and passed to the Butler family in 1375, it's one of Ireland's largest castles. In 1599 the Earl of Essex shattered its walls with cannon fire, an event illustrated by a large model. The impressive Banqueting Hall has a huge set of antlers pinned to its white walls, and you can climb the Keep.
The castle, originally built to protect a salmon fishery and important river crossing, eventually surrendered to Cromwell in 1650 without a struggle; its future usefulness may have discouraged the usual Cromwellian 'deconstruction' – it is largely intact and still formidable. It was restored in the 1840s and again in the 1960s when it came under state ownership.
A 15-minute audiovisual presentation puts Cahir in context with other Irish castles. The buildings within the castle walls are sparsely furnished, although there are good displays, including an exhibition on 'Women in Medieval Ireland'. There are frequent guided tours.