Greencastle
Greencastle at the entrance to Carlingford Lough in County Down, Northern Ireland, is a thirteenth-century royal castle built by Hugh de Lacy in 1261 to control the entrance to Carlingford Lough and the trade routes between Ireland and England. The castle faces its counterpart Carlingford Castle in County Louth across the narrow lough, forming a pair of castles controlling this strategically important sea inlet. The substantial remains of the great tower and gatehouse are in the care of the Historic Environment Division and are freely accessible. The position at the mouth of the lough with views toward the Cooley Mountains in the Republic of Ireland and the Mountains of Mourne behind provides one of the most scenic settings of any castle in County Down.