Inishowen is a peninsula in Co Donegal. It is the largest peninsula in Ireland and is known for its picturesque scenery and rich history. The peninsula includes Ireland's most northerly point, Malin Head, along with Lagg sand dunes, some of the highest in Europe. The Grianan of Aileach, a ringfort that served as the royal seat of the Kingdom of Ailech, stands at the entrance to the peninsula. The peninsula measures 884.33 square kilometres (218,523 acres) and is bordered to the north by the Atlantic Ocean, to the east by Lough Foyle and to the west by Lough Swilly. While mainly in Donegal, the south-eastern part of the peninsula lies in Derry in Northern Ireland. The peninsula is separated from the rest of Northern Ireland by the River Foyle. The main towns and villages of Inishowen are: Ballyliffin, Buncrana, Bridgend, Burnfoot, Burt, Carndonagh, Carrowmenagh, Clonmany, Culdaff, Dunaff, Fahan, Glengad, Gleneely, Greencastle, Killea, Malin, Malin Head, Moville, Muff, Newtowncunningham, Redcastle, Quigley's Point and Urris. Inishowen has several harbours, some of which are used for commercial fishing purposes, including Greencastle, Bunagee and Leenan. A seasonal ferry service crosses the Foyle, connecting Greencastle with Magilligan in Derry, while another crosses the Swilly, connecting Buncrana with Rathmullan. The village of Fahan has a privately built marina. There are several small outlying islands off the Inishowen coast, most notably Inishtrahull and Glashedy islands, both uninhabited. Inch, located in Lough Swilly, is technically no longer an island, as it has a causeway connecting it to the mainland at Tooban, south of Fahan. The Inishowen 100 tourist route is an approximately 100-mile signposted scenic drive around the peninsula. It takes in or passes nearby most of the tourist attractions and places of interest on the peninsula. It starts and ends in Bridgend where there is a large map and information boards.