Croaghaun (Irish: Cruachán) is a mountain in County Mayo, Ireland. At 688 metres (2,257 ft), it has the highest cliffs in Ireland and Great Britain as well as the third highest sea cliffs in Europe (after Hornelen, Norway and Cape Enniberg, Faroe Islands).
Croaghaun 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. The views from the top of the cliffs are breathtaking, and the unusual corries and unique rock types make this location desirable to hikers. The cliffs are not reachable by car and visitors must either park at Keem beach and trek from there; park at the supply lake on the way to Keem bay; or go by boat.
The Croaghaun cliffs are home to two families of peregrine falcons (RTÉ, 2008). September and October are the best time to see the fastest creatures on Earth here, as they teach their young to fly. Metamorphic, quartz-laden gems may be observed, along with Mediterranean heathers and the waters of the Atlantic. It is common to see shoals of bottle-nosed dolphins and basking sharks, once a source of revenue for Achill Island (BBC, 2009). Porpoises are found in large numbers. Killer whales, humpback whales, and other whales have been sighted. 
- ^  Mountainviews, Croaghaun
- ^ Clarke, Harold (1970). Ireland in Color. New York: Viking Press, p. 108. ISBN 978-0-670-40093-5.
- ^  Western People - Blue Whale spotted off Achill
Coordinates: 53°58′52″N 10°12′14″W / 53.981°N 10.204°W