Cheju Island, also called Quelpart Island, Korean in full Cheju-t’ŭkpyŏlchach’i-do or Jeju-teukbyeoljachi-do, island and (since 2006) special autonomous province of South Korea. The province, the smallest of the republic, is in the East China Sea 60 miles (100 km) southwest of South Chŏlla province, of which it once was a part. The provincial capital is the city of Cheju.
Oval in shape, Cheju Island measures 40 miles (64 km) from east to west and 16 miles (26 km) from north to south. The island is composed of a core of volcanic material that rises symmetrically to the crest of Mount Halla (6,398 feet [1,950 metres]), which has a lake in its crater. The mountain and its surrounding area are a national park. Hundreds of crater-formed hills from which volcanic material once flowed, seaside precipices with waterfalls, and lava tunnels (or tubes) are international sightseeing attractions. The island’s lava tubes and certain other volcanic formations (including Mount Halla) were collectively designated a UNESCO World Heritage site in 2007. Cheju is bathed in warm currents, and its oceanic climate supports some subtropical plants.