https://heritageireland.ie/places-to-visit/cahir-castle/

https://www.openstreetmap.org/way/162602114 Street view (where you can walk right in!) https://goo.gl/maps/5ZUodtgRvanv1Bw27

Open all year except for a few days around Christmas.

Cahir Castle (Irish: Caisleán na Cathrach), one of the largest castles in Ireland, is sited on an island in the river Suir. It was built from 1142 by Conchobar Ua Briain, King of Thomond. Now situated in Cahir town centre, County Tipperary, the castle is well preserved and has guided tour and audiovisual shows in multiple languages. Construction

The castle was sited on and near an earlier native fortification known as a cathair (stone fort), which gave its name to the place. The core structure of the castle dates to construction in the 13th century by the O’Brien family. The castle was built in two parts, with the side now by the street being built 200 years before the side now housing the audio-visual show.

Granted to the powerful Butler family in late 14th century, the castle was enlarged and remodelled between the 15th and 17th centuries. It fell into ruin in the late 18th century and was partially restored in the 1840s. The Great Hall was partly rebuilt in 1840.