The castle is one of the largest in Ireland, on an island on the River Suir in Tipperary, in Cahir town centre. It was constructed by Conor O'Brien, Prince of Thomond in 1142, and would become part of the Butler family estates (so called because they made a fortune handling the wine imports ('hic) and were of Anglo Norman descent, and who would found the influential House of Ormonde, which would be influential when it all went pear shaped in the C17th).
The castle was sited on and near an earlier native fortification known as a cathair (stone fort), which gave its name to the place. Like most castles, there is a central ward/keep, then later outer walls were constructed.
Granted to the powerful Butler family in late 14th century, the castle was enlarged and re-modelled between the 15th and 17th centuries. It fell into ruin in the late 18th century and was partially restored in the 1840s.
Essex besieged it in 1599, before losing his head to Elizabeth's rage. Murrough O'Brien (Lord Inchquin - who, if I remember my history, changed sides 2 or 3 times during the English Civil War's resultant rebellion in Ireland - and was a distant relative of the castle's Norman builder) . It was surrendered to Cromwell in 1650.
Of note is the fact that parts of Excalibur were filmed here, as well as Barry Lyndon (before Mr. Kubrick was 'asked' to leave apparently...they were clearly turbulent times). The Tudors has also recently had parts filmed here. Not Game of Thrones however (probably too expensive for 'em when they can get cheap extras in N.Ireland grumble...grumble).
You can try getting in using this method, but to be honest, it's easier just to pay a few Euros ...
A great visit and the castle is in superb condition; recommended - especially so when you consider the great diorama shown last time.
'Are those buggers trying to get in without payin' Da?'
(I need very little encouragement to include pics of Cherie Lunghi - and yes, that bloke was in Star Trek.)