The Boryeong Undersea Tunnel is a 6.9 km road tunnel connecting Daecheon Port in Boryeong and Wonsan Island near Anmyeondo. It opened in December 2021 and cut a trip that took 90 minutes down to 10 to 15 minutes. Inside, a marker shows the 80 m point below sea level, and speed cameras at 70 km per hour sit at the entrance and exit. Like an ordinary tunnel, it offers no view of the sea.