Fort Dunree sits on a rocky promontory on the west coast of Inishowen, reached over a natural cleft in the rock. It was built during the Napoleonic Wars to guard Lough Swilly, rearmed in the 1890s, and manned with six-inch guns in the First World War. After independence it remained one of the British-held "Treaty Ports" until 1938, the last time any territory was handed over to the Irish state. The Irish Army trained here until 1990.
Today it is a military museum, opened in 1986, with restored guns, an old camp and displays on the birds and sea life of the lough, plus a café and walking trails. The setting above Lough Swilly is as good a reason to come as the guns. It is open daily; adult admission was €10 in 2026.