Standing on top of a hill at the southern entrance to Inishowen, the Grianan of Aileach is a stone ringfort that was once the royal seat of the over-kingdom of Ailech. It was the seat of high kings, including the Meic Lochlainn, who held power here for centuries. A Limerick king is said to have come north to destroy it, ordering each of his soldiers to carry away a single stone to prevent rebuilding. The fort was restored in the nineteenth century, and recent decades have seen some damage with the partial collapse of the south wall. From its top, on a clear day, you can see across Lough Swilly to Donegal town and east toward Derry. The view explains the choice of site: anyone moving through the peninsula could be seen from here.

The Norman Earldom of Ulster expanded into Inishowen in the thirteenth century, founding Greencastle on the Foyle. After the Bruce invasion in the early fourteenth century, the O Dochartaigh (O'Doherty) clan gradually conquered Inishowen as they lost their original homeland in the Laggan to the east. The main castle ruins of the peninsula come from this period or shortly after: Carrickabraghy on the Isle of Doagh, the Norman Castle at Greencastle, Inch Castle, Buncrana Castle, and Elagh Castle. In 1608, Sir Cahir O'Doherty, the last great Lord of Inishowen, launched his rebellion by burning Derry. He was twenty-one years old and was killed within months at Kilmacrennan. His lands were granted to Arthur Chichester, whose descendants kept them for centuries.

Malin Head, on the small peninsula at the top of Inishowen, is the northernmost point of the Irish mainland. Dunalderagh, its sharp tip, lies several kilometres further north than anywhere in Northern Ireland (those extremes being Benbane Head near Giant's Causeway and Rathlin Island off Ballycastle). The head is exposed to the full force of Atlantic weather. Bird-watching is the main attraction. There is a Napoleonic-era lookout tower, an Eire 80 sign etched in 1943 to alert wartime pilots they were approaching the neutral Republic, and cliffs that funnel storm-driven spray through clefts like Pólifreann (Hell's Hole). Ten kilometres further north is Inishtrahull, Ireland's most northerly inhabited island until 1929. The keepers of its lighthouse stayed until 1987, when it was automated.

On the evening of 11 July 2010, seven young local men and an older pensioner died in a road accident on the R238 just outside Clonmany. The youngest victims were teenagers. The crash, which involved a single vehicle, received national and international media coverage. It became Ireland's deadliest road accident of the modern era. The funerals stretched over days. Inishowen is a small place by population, even now: about forty-five thousand people across the whole 884-square-kilometre peninsula at the 2016 census, of whom about 6,785 live in Buncrana, the largest town. In a community that small, eight deaths in a single night ripples through every relationship. The memorial along the road is still tended.

The Inishowen 100 is a signposted scenic drive of approximately one hundred miles around the peninsula's coast. It begins at Bridgend, runs north along Lough Swilly through Inch Island, Fahan, Buncrana, and Fort Dunree, turns inland to Mamore Gap, then back to the coast at Tullagh Bay, Clonmany, and Ballyliffin. From there it crosses to Carndonagh and turns north again through Malin to Malin Head. The eastern leg returns south along Lough Foyle through Culdaff, Kinnagoe Bay, Greencastle, Moville, and Muff. The whole route coincides for much of its length with the Wild Atlantic Way, the 2,500-kilometre coastal route from Malin Head all the way to Kinsale in County Cork. The two routes share their starting point. The road numbers tell you which one you are on. The view tells you it doesn't really matter.