Udo, also known as U Island and sometimes Soseom, is an island in Jeju Province, South Korea. It is 2.8 km off the coast of Jeju Island, and is the second-largest island in the province. The island is one of Jeju's most popular destinations, with 2.23 million visitors in 2016. It is known for its scenic beaches, sheer rocky cliffs, and sea caves. It is reachable by f…Udo, also known as U Island and sometimes Soseom, is an island in Jeju Province, South Korea. It is 2.8 km off the coast of Jeju Island, and is the second-largest island in the province. The island is one of Jeju's most popular destinations, with 2.23 million visitors in 2016. It is known for its scenic beaches, sheer rocky cliffs, and sea caves. It is reachable by ferry, and bikes and public transit are available on the island.