Sea-stack off Downpatrick Head

Dun Briste, an impressive sea-stack, estimated to be approximately 50 metres in height, stands 80 metres off Downpatrick Head, in the town-land of Knockaun, east of Ballycastle, Co. Mayo. The cliffs in the area, including the stack, were formed in the Lower Carboniferous period, a geological term applied to a time c. 350 million years ago, when the sea temperatures around Ireland were much higher than today. [Source]