Okubo Mabu is one of the most impressive mine tunnels within the UNESCO World Heritage Site of Iwami Ginzan Silver Mine and its Cultural Landscape in Oda City, Shimane Prefecture. Tunnels excavated for silver mining are known in Japanese as “mabu,” and approximately 1,000 mine tunnels of various sizes have been identified throughout the Iwami Ginzan area. Among them, Okubo Mabu is one of the largest and provides a powerful glimpse into the scale of silver mining that supported the prosperity of Iwami Ginzan.
The highlight of Okubo Mabu is the enormous space that opens up inside the mine. One section of the tunnel contains a vast underground chamber measuring approximately 20 meters high, 30 meters deep, and 15 meters wide. Standing inside this immense cavity makes it possible to appreciate the remarkable scale of mining operations carried out here.
The size of the chamber is particularly impressive considering that much of the excavation was carried out by hand. Marks left by miners using chisels and hammers during the Edo period can still be seen inside the tunnel, offering a tangible connection to the people who once worked underground.
Mining technology changed with the arrival of the Meiji era. Mechanical excavation methods were introduced, and parts of the mine were expanded using newer techniques. The coexistence of excavation traces from different periods makes Okubo Mabu especially valuable as a historical site.
The name Okubo Mabu is traditionally associated with Okubo Nagayasu, the first magistrate who governed Iwami Ginzan during the early Edo period.
According to local tradition, Okubo Nagayasu once entered the mine while riding a horse and carrying a spear. Although it is uncertain whether this actually happened, the story has been passed down as an illustration of just how spacious the mine was believed to be.
The legend adds another fascinating layer to the site, suggesting that the scale of the underground passages was remarkable even by the standards of the time.
Mining at Okubo Mabu began in the latter part of the 16th century, and the mine remained in use for centuries until 1896. Its location deep in the mountains helped preserve numerous traces of mining activity in remarkably good condition.
Inside the tunnel, visitors can see traces associated with the railway equipment once used to transport materials, including the remains of railroad sleepers and the metal spikes known as “inu-kugi” that were used to secure the rails.
These old rail spikes are particularly rare in Japan and have retained their original form even after more than a century. The cool, humid environment of the mine, combined with limited exposure to the outside air, helped protect wooden materials from decay and reduced corrosion of metal objects.
For safety reasons, Okubo Mabu can be visited only as part of a guided tour. The entire tunnel extends for approximately 900 meters, although only a portion is open for visitors. Advance reservations are required.
Walking through the mine while listening to a guide’s explanations provides a deeper understanding of the history of silver mining, the techniques used to excavate the mountain, and the lives of the people who worked in this demanding environment.
The temperature and humidity inside the mine remain relatively stable throughout the year. In recent years, this unique underground environment has also been used to mature Stollen, a traditional German Christmas fruitcake. This unusual modern use offers an interesting connection between the mine’s historical environment and contemporary local initiatives.
The development of Iwami Ginzan was closely connected to the geological conditions created by the ancient volcano known as Mt. Sennoyama. Volcanic activity approximately 1.5 million years ago created porous and relatively soft geological formations that provided favorable conditions for hydrothermal fluids carrying minerals such as silver and copper.
These mineral-rich hot fluids traveled upward through cracks in the surrounding rock. As they cooled near the Earth’s surface, they deposited minerals and formed the ore veins that eventually became the target of mining operations.
Because some of these silver deposits were located relatively close to the surface, miners could extract the ore using comparatively simple tools such as chisels and hammers. The geological characteristics of the area therefore played an important role in making Iwami Ginzan a major silver-producing region.
Okubo Mabu is far more than an abandoned mine. It is a valuable cultural heritage site where geology, mining technology, and human history come together.
The enormous underground chamber reveals the scale of excavation, while the marks left by hand tools show how earlier generations worked through solid rock. Later modifications and railway-related remains demonstrate how mining technology evolved over the centuries.
At the same time, the geological story beneath the mine explains why silver was found here in the first place. Together, these elements allow visitors to understand Iwami Ginzan from both a natural and human perspective.
Joining a guided tour of Okubo Mabu offers a rare opportunity to step into an underground landscape that preserves centuries of mining history. The immense chambers, excavation marks, railway remains, and geological features provide a vivid impression of the extraordinary effort required to extract silver from the mountains of Iwami.
When visiting the Iwami Ginzan area, be sure to explore Okubo Mabu and experience the remarkable underground world that supported the prosperity of the silver mine. Beneath the mountains lies a fascinating record of the natural forces that created the mineral deposits and the generations of people whose knowledge, labor, and technology transformed them into one of Japan’s historic silver-mining centers.