Achill Island in County Mayo is the largest island off the coast of Ireland, and is situated off the west coast.Croaghaun is a mountain in County Mayo, Ireland. At 688 metres (2,257 ft), it has the highest sea cliffs in IrelandCroaghaun is the most westerly peak of Achill Island, and its highest mountain. Its cliffs lie on the northern slope of the mountain. The cliffs at Croaghaun can only be seen by hiking around or to the summit of the mountain, or from the sea. They are part of a sequence of sheer rock faces which start south of Keem Bay and loop around the uninhabited northwest of the island, by Achill Head and Saddle Head, and east to Slievemore, occasionally dropping vertically into the waters of the Atlantic Ocean.