Inaccessible Island is an extinct volcano (last active six million years ago) with Cairn Peak reaching 449 m. The island is 14 km2 (5.4 sq mi) in area, rising out of the South Atlantic Ocean 45 km (28 mi) south-west of Tristan da Cunha.It is part of the archipelago of Tristan da Cunha which is part of the overseas territory of the United Kingdom known as Saint Helena, Ascension and Tristan da Cunha.