Dungarvan Castle is an Anglo-Norman fortification founded in the 12th century to safeguard the entrance to the strategically important harbour and mouth of the River Colligan. The earliest structure is a rare polygonal shell keep, surrounded by an enclosing curtain wall, a corner tower, and a gate tower.

Inside is a British military barracks, dating from the first half of the 18th century. They were burned down by occupying IRA forces during the Irish Civil War but restored with the foundation of the Garda Siochana in 1922. The building remained in use as a Garda station until 1987. It is now a museum.