Okubo Mine Tunnel
Okubo is the largest tunnel system at Iwami Ginzan and one of the two main mining tunnels open to visitors on a regular basis. It is one of the most thoroughly excavated parts of the silver mine, having been mined from the late 1500s until the Meiji era (1868–1912) and enlarged repeatedly over the centuries. Distinguished by its high entrance, the tunnel bears the name of Okubo Nagayasu (1545–1613), the first magistrate appointed by the Tokugawa government to oversee Iwami Ginzan.
Several smaller shafts branch out from the main tunnel, which is as high as 5 meters in places. These were dug to follow the veins of silver, traces of which are still visible here and there along the walls. There are also vertical shafts, some for ventilation and others that were used to route groundwater outside. The walls of the main tunnel are smooth where they were shaped by chisels and hammers. The tunnel was widened in the Meiji era to accommodate carts, so other parts of the walls bear marks of rough excavation techniques, including the dynamite used to widen the passage. Some cart rail crossties from this time are still visible on the ground.
Guided tours of the Okubo tunnels are given on weekends and public holidays from April to November. In winter the tunnels become the domain of hibernating bats, which can be spotted flying around inside year-round.