Sakunouchi is the heart of the Iwami Ginzan mining district, the area where the silver was dug, and the name roughly means inside the fence. In the sixteenth and seventeenth centuries, the mining area was enclosed and controlled, and the people who worked within it were registered and monitored, so that nothing valuable left without notice. Today the site is a quiet forested valley with a footpath, a stream and the openings of many old tunnels, some of them hundreds of years old.
The tunnels are called mabu, and the best known, Ryugenji Mabu, is open to visitors for a short walk. It is a narrow, damp passage dug by hand, with chisel marks still visible on the walls, side shafts leading off into darkness and small niches where lamps were placed. The air is cool and still, and the sound of dripping water is constant. It gives an immediate and unvarnished sense of how hard the work was, and how small the miners were by the standards of today. A short way along the valley stand the remains of a refining site, with terraces and foundations in the trees.
Getting here by bike means leaving the machine behind. The valley road from Oda is narrow, wooded and shaded, with a few tight bends and light traffic, and visitors park at the lots at the edge of the district, then walk or cycle in. The paths are well made but wet and slippery in rain, so bring sensible shoes and a light waterproof. The tunnel is cool even in summer, so a thin extra layer is welcome.
Fuel is in Oda, about eleven kilometres away, with little available in the valley itself. There are a few modest cafes and shops in Omori, but come with water and a snack. Visit early in the day, before the coaches, and you may have the tunnel to yourself. The ride from here continues on a long road toward Itsukushima, so keep an eye on time, and leave plenty of daylight for the journey.