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]

Glorious Sea Cave – Algarve, Portugal

Apparently this cave is quite near Benagil Beach in Algarve, Portugal. A sea cave, also known as a littoral cave, is a type of cave formed primarily by the wave action of the sea. The primary process involved is erosion. Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. [Source]

Sea Cliffs, Normandy, France

Although the 80-mile stretch of sheer cliffs between Dieppe and Etretat, in upper Normandy, is mirrored by those of the English coast of Dover, pointing to their shared geological origin, no other section of the French shoreline resembles the unique breathtaking seascape of La Côte d'Albâtre—the Alabaster Coast. The section around Fécamp also goes by the poetic name of le Pays des Hautes Falaises (high cliff country) conjuring up the flavor of salty air and the shrieks of circling gulls. Unsurprisingly, the coast attracted a plethora of famous painters and writers in the 19th century, especially the Impressionists, who were captivated by its ever-changing light. [Source]