Seikan Tonneru (Japan)

The Seikan Tunnel (Japanese: 青函トンネル, Seikan Tonneru or 青函隧道, Seikan Zuidō) is a 53.85-kilometre (33.5-mile) dual-gauge railway tunnel in Japan, with a 23.3-kilometre (14.5-mile) segment running beneath the seabed of the Tsugaru Strait, which separates Aomori Prefecture on Honshu, Japan's main island, from the northern island of Hokkaido. The tunnel's track level lies approximately 100 metres (330 ft) below the seabed and 240 metres (790 ft) below sea level. Following several decades of planning and construction, the tunnel opened on 13 March 1988. The Seikan Tunnel forms part of the standard-gauge Hokkaido Shinkansen as well as the narrow-gauge Kaikyō Line operated by the Hokkaido Railway Company (JR Hokkaido). Its name, "Seikan," is derived from the on'yomi readings of the first characters of Aomori (青森), the nearest major city in Honshu, and Hakodate (函館), the nearest major city in Hokkaido. By total length, the Seikan Tunnel is the world’s longest undersea tunnel, surpassing even the Channel Tunnel (although the latter has a longer undersea section at 37.9 kilometres (23.5 mi) vs 23.3 kilometres (14.5 mi) for the Seikan Tunnel). It is also the deepest railroad tunnel below sea level and was the deepest transport tunnel of any kind until Norway's Hitra Tunnel opened in 1994. It is the second longest main-line railway tunnel following Switzerland’s Gotthard Base Tunnel, which began operations in 2016.