The Hisatsu line[1] in Japan was built through pretty insane terrain to make it protected from coastal attacks after the Russo-Japanese war. [1] https://en.wik

The Hisatsu line[1] in Japan was built through pretty insane terrain to make it protected from coastal attacks after the Russo-Japanese war. [1] https://en.wikipedia.org/wiki/Hisatsu_Line https://en.wikipedia.org/wiki/Hisatsu_Line