Tanna Tunnel, Railway tunnel between Atami and Kannami, Japan.
The Tanna Tunnel is a railway bore in Shizuoka Prefecture that runs through the Hakone mountain range, linking Atami and Kannami. It passes beneath dense volcanic rock and extends just under eight kilometers through one of the most complex geological zones in the region.
Construction began in 1918 and required 16 years until completion in 1934. Two severe collapses claimed the lives of 67 workers, making this one of the most difficult engineering projects of the era.
The name refers to the town of Tanna, now part of Kannami. The route follows one of the oldest trade corridors linking the capital region with the western provinces.
The bore is part of the Tōkaidō Main Line and trains pass through it while traveling between Tokyo and Osaka. Passengers usually notice only the darkening of windows and a slight pressure change in the ears.
The excavation uncovered multiple active fault lines that allowed hot springs to seep into the bore. Engineers had to redirect thermal water to keep the interior temperature bearable.
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