The Seikan Tunnel (青函トンネル Seikan Tonneru or 青函隧道 Seikan Zuidō) is a railway tunnel in Japan, with a long portion under the seabed. The track level is about below the seabed and below sea level. It travels beneath the Tsugaru Strait—connecting Aomori Prefecture on the main Japanese island of Honshu with the northern island of Hokkaido—as part of the Kaikyo Line portion of the Hokkaido Railway Company (JR Hokkaido)'s Tsugaru-Kaikyō Line. The name Seikan comes from combining the on'yomi readings of the first characters of , the nearest major city on the Honshu side of the strait, and , the nearest major city on the Hokkaido side.