Located 23 kilometres off the coast of Taiwan, almost directly east of Taitung City, Green Island is Taiwan's seventh largest island. In an effort to promote tourism and scuba diving activity on the island, a local scuba diver installed a mailbox in 6 metres of water off the coast. He was forced to removed the unauthorized mailbox but the local government, in cooperation with Chunghwa Post decided to install an official mail box in 2018. Local divers took responsibility for scheduled mail pick-ups. Shaped like the pygmy seahorse,Hippocampus colemani--a symbol for the region, the mailbox is located under 11.5 metres of water, giving it the distinction of being the world's deepest mailbox when it was installed.

Lu Tao lighthouse, the subject of a definitive stamp issued by Taiwan on May 20, 1991, was originally constructed with American assistance after the islanders rescued the passengers and crew from the S.S. President Hoover after it ran aground on reefs off the island in 1937.