Tanna Tunnel
The 143rd longest tunnel in the world
Tanna Tunnel (Tanna-tonneru) is a railroad tunnel in Shizuoka Prefecture, Japan operated as part of JR Central’s Tōkaidō Main Line. When opened in 1934 this 7.8 km long tunnel shortened the trunk route between Tokyo and Kobe by 11.7 kilometres and reduced the ruling gradient between Kozu and Numazu from 2.5% (1 in 40) to less than 1% (1 in 100). It superseded the original route (now the Gotemba Line) which could be described as a detour round the mountains between Atami and Numazu.
Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).