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.