Jeju Undersea Tunnel

The Jeju Undersea Tunnel is a proposed undersea tunnel project to connect the South Korean provinces of South Jeolla and Jeju across the Jeju Strait, with intermediate stops at the islands of Bogildo and Chujado. The proposed 73 km tunnel is projected to take 11 years to complete at an estimated cost of 14.6 trillion South Korean won (11.2 billion US Dollars).

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).

Other tunnels in South Korea

Delaware Aqueduct United States · 137 km Päijänne Water Tunnel Finland · 120 km Orange–Fish River Tunnel South Africa · 82.8 km Ishikawa Tunnel Japan · 78.5 km Brenner Base Tunnel Austria · 64 km Mont d'Ambin base tunnel France · 57.5 km Gotthard Base Tunnel Switzerland · 57.09 km Hong Kong–Zhuhai–Macau Bridge China · 55 km