Three Castle Head, Co. Cork, is truly one of the hidden gems of Ireland's Atlantic coast. It is privately owned, but (as far as I know) walkers are permitted to roam from the road up to Dunlough Castle, which is just visible here in front of the lake on the head.
The first castle was built here in the 13th century, although the ruins you see here are probably from the 15th century. The ruins include three keeps of dry stone construction and the remains of a curtain wall. The lake is probably manmade, as another wall at the eastern end appears to serve as a dam.
The land on the very left of the frame is the Sheep's Head peninsula, the smallest of the five major peninsulas that make up the coast of west Cork and Kerry.
(You can buy a print of this photograph here: https://buff.ly/2KpaKEB)