Iki Island
The strait is the channel to the east and southeast of Tsushima Island, with the Japanese islands of Honshu to the east and northeast, and Kyushu and the Gotō Islands to the south and southeast. It is narrowest south-east of Shimono-shima, the south end of Tsushima Island proper, constricted there by nearby Iki Island, which lies wholly in the strait near the tip of Honshu. South of that point Japan's Inland Sea mingles its waters through the narrow Kanmon Strait between Honshu and Kyushu, with those of the Eastern Channel, making for some of the busiest sea lanes in the world.