Grianan of Aileach , Carrowreagh , County Donegal
Set on top of 800ft Greenan hill , this fort , built around 1700BC , possibly as a druidic sun temple and occupied until the 12th century , offers views over both loughs Swilly and Foyle.
Grianan means ‘sun palace’ and the kingdom of Aileach consisted of County Donegal and most of counties Derry, Tyrone and Armagh , over which the O’Neill clan , the Kings of Ulster , ruled.
It is thought that the O’Neills built the stone cashel in early Christian times as their royal seat and stronghold. The entire enclosure , including outlying Eastern banks , covers 4 acres.