King John's Castle (Irish:Caisleán Luimnigh) is a thirteenth century castle located in the City of Limerick/Luimneach and is on King's Island overlooking the River Shannon (Irish: Abha na Sionainne). Also on the island is St Mary's Cathedral which is over 800 years old. Kings Island (Inis Sibhtonn) was a Viking stronghold before the building of the castle and Viking sea-king, Tomrair mac Ailchi, built the first permanent Viking stronghold there in 922 AD. The castle is open to the public and has exhibitions of the history of the site.
Links: Kings John's Castle Shannon Heritage
Image: King John’s Castle in Limerick courtesy of The Irish Times