The Grianan of Aileach (Irish: Grianán Ailigh) is a hillfort sitting on 801 ft high Greenan Mountain at Inishowen in County Donegal. The summit dominates the neighbouring counties of Londonderry, Donegal, and Tyrone. It has been identified as the seat of the Kingdom of Ailech and one of the royal sites of Gaelic Ireland.
Grianán of Aileach is located high upon a hilltop that lies between the upper reaches of Lough Swilly and Lough Foyle.
The main structure is a stone ringfort, thought to have been built in the sixth or seventh century.
The ringfort was mostly destroyed by the King of Munster in 1101, but was later restored in 1870.
The walls are about 15 feet thick. Inside are three terraces linked by a series of steps.
A visitor stands at the top of the wall and takes in the stunning scenery at this wild and windswept location.