Construction to penetrate one of the two tubes of the nation’s longest undersea tunnel, the Boryeong Undersea Tunnel in South Chungcheong Province has been completed seven years after ground was first broken for the project.

The Ministry of Land, Infrastructure, and Transport announced that construction to penetrate the tube bound for Boryeong was completed on Monday. The move came after the other tube bound for Wonsan Island was penetrated earlier in February. 

The Boryeong undersea tunnel, under construction since 2012, is the world’s fifth longest underwater tunnel. 

An eight-kilometer section, linking Daecheon Port and Wonsan Island, which includes the underwater tunnel, is slated to open by the end of 2021, while a six-point-one kilometer-long bridge connecting Wonsan Island and Anmyeon Island will open later this December.