Dun Briste is 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. On the adjoining Downpatrick headland, several archaeological monuments may be seen, and these range in type from Bronze-Age ring-barrows, early ecclesiastical sites, the remains of a promontory fort, to a more modern coastguard "watch-house" of W.W.2 vintage.
