One of the finest Norman castles in Ireland, Carrickfergus Castle is sited along the harbour front, controlling the seashore. Probably constructed by John de Courcey sometime around 1180, it is sited on a large rock jutting out into the sea. The earliest part of it is the massive four story keep entered at first floor level. There is an inner courtyard inside the outer wall which was the original outer defence. After the capture of the castle by King John, he added the outer wall, towers, and the gatehouse.
The castle was seized again in 1689 for King William and later by the French in 1760. Since that it has acted as prison, armoury and air raid shelter and is now open to the public.