Clare Island lies at the entrance to Clew Bay in County Mayo, some 5km from the west coast of the Irish mainland. The dominating feature of the island is a ridge that runs east to west, attaining a height of 465m at Croaghmore and forming precipitous sea cliffs along the northern shore. The island's rock surfaces have been scoured by glaciers in the last Ice Age and a mass of glacial sediments has been dumped on its southern slopes. The cliffs of Clare Island are listed as an area of international scientific importance, sheltering rare arctic-alpine plant communities and seabird breeding colonies.

Clare Island has a long history of habitation from at least 3500 BC. There is an abundance of Bronze Age sites, a 13th-century Cistercian Abbey adorned with painted frescoes and the island harbour is guarded by the fort of Grace O'Malley, the battling pirate queen of Elizabethan times.