Legend has it that before the Ao no Doumon tunnel was built, worshipers had to climb steep cliffs to reach a local shrine, a perilous path that claimed many lives. In the Edo period, a Buddhist monk named Zenkai, who had once committed a murder, resolved to create a safer passage as atonement. Starting at the age of 49, he devoted thirty years of his life to manually excavating the 185‑metre tunnel, using only a hammer and chisel.