Seikan Tunnel (lowest railway)

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The Seikan Tunnel (青函トンネル Seikan Tonneru or 青函隧道 Seikan Zuidō) is a 53.85-kilometre (33.46 mi) railway tunnel in Japan, with a 23.3-kilometre (14.5 mi) long portion under the seabed. The track level is about 140 metres (460 ft) below the seabed and 240 m (790 ft) below sea level. It travels beneath the Tsugaru Strait — connecting Aomori Prefecture on the Japanese island Honshu and the island Hokkaido — as part of the Kaikyo Line of Hokkaido Railway Company. The name Seikan comes from combining the on'yomi readings of the first characters of Aomori (青森^?) and Hakodate (函館^?), the nearest major city on the Hokkaido side.

• http://en.wikipedia.org/wiki/Seikan Tunnel