Episode 7: The Grianan of Aileach.
Its walls are about 4.5 metres (15 ft) thick and 5 metres (16 ft) high and it encloses an area of 23.6 meters (77 ft). A magnificent ancient structure that was renovated in the 1870s and provides some of the best views in the country.
This circular fort sits atop Greenan mountain (244m) in Inishowen, Donegal. Activity at the site has been dated to 1700BC although the main stone ringfort structure was likely built in the 6th or 7th century by the Northern Uí Néill. It has been identified as the seat of the Kingdom of Ailech and one of the royal sites of Gaelic Ireland.