There is a documentary film named "Horumaika Tebori Nakayama-Zuido no Kiroku (掘るまいか 手掘り中山隧道の記録)" directed by Shinichi Hashimoto [ja].
Komatsukura settlement, Yamakoshi Village is surrounded by mountains and its residents have to go to Koide Town through Hirokami Village where cross from Nakayama Pass (中山峠, Nakayama touge) in order to go shopping or to hospital until 1949.
In the winter, it was hard to pass since snow fall is in excess of 4 m and sometimes there are snowstorm.
The residents had dug it by human power using pickaxes without hope the future.
In 1949, pasting more than fifteen years from starting construction, the tunnel was opened to the opposite side.