King John's Castle is an Anglo-Norman fortification founded in 1185. It was built in a very strategic location at the mouth of the River Colligan.

From here ships could be anchored, and soldiers could command the narrow strip of land to the south of the Comeragh Mountains, which linked East and West Waterford. It was one of the few royal castles built in Ireland in the 1200s. During the Irish Civil War, the barracks were taken by the IRA forces who set fire to it before leaving in August 1922.

With the foundation of the Garda Siochana in 1922 the building was restored and used as the local Garda Station until 1987. It fell into disrepair, but today it has been restored and is managed by Dúchas, the Heritage Service, who provides guided tours, an audio-visual show and exhibitions during the summer months.