The Seikan tunnel it is the longest tunnel in the world and it can be crossed by taking a train from Aomori in the north of the Island of Honshu and it goes below the sea to the Island of Hokkaido. I crossed this tunnel twice, one in my way up north to Sapporo and a few days later on my way back to Tokyo. The first time I crossed it I was on expectation, however information about the tunnel was given only in Japanese, like information about the construction of the tunnel, length and depth. Here is some data I got from my travel guide, the tunnel is 53.8 km in length of which 23.3 km lie under the sea of the Tsugaru Strait, the deepest point of the tunnel is 240m below sea level. It took about 22 minutes to cross it, after that there are more tunnels on both sides but these tunnels are short. I also read that there are two train stations below the sea, that are used in case of emergency, I tried to take a photo but the train speed is so fast that it is impossible to get a picture, however I got the picture in my head and the experience of crossing the Seikan tunnel.
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