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Arafune Fuka is a storage facility for silkworm eggs (eggs of the silkworm) located in Shimonita Town, Gunma Prefecture, which was actively used from the Meiji to the Taisho era. By utilizing the natural topography, the facility harnessed the cold air blowing from rock crevices to maintain a constant temperature, a technique used to control the hatching timing of the silkworms. As a component of the UNESCO World Heritage site 'Tomioka Silk Mill and Related Sites', it is a vital cultural heritage that tells the story of the sericulture industry that supported Japan's modernization. The scale of the facility, which boasted one of the largest storage capacities in the country, and its ingenious structure utilizing natural forces, showcase the advanced technological capabilities of that era.
During the Meiji era, securing a stable supply of silkworm eggs was essential to support the production of raw silk, Japan's primary export at the time. Controlling the hatching period through temperature regulation was key to increasing productivity. Arafune Fka was developed around 1905 (Meiji 38) to 1914 (Taisho 3). Built by the father-and-son duo Seitaro and Chiju Niwa, the facility created a stable environment regardless of the season by using natural cold air. At its peak, the silk industry driven by such technology contributed significantly to global trade. Today, the preserved stone structures serve as precious historical monuments documenting the development of modern sericulture.
The most striking feature is the sophisticated stone-built wind cave structure. Originally, a building similar to a storehouse was built above the cave, and a three-layer structure (two underground levels and one ground level) was used for temperature control. Although the upper building is gone, the remaining stone ruins allow visitors to appreciate the ingenuity of the past, where people managed to capture and utilize natural cold air efficiently. Nearby sites like the 'Higashidani Fuka' also form a historical field that narrates the history of the silk industry. Occasional guided tours provide deeper insights into the structure and historical context.
Since Arafune Fuka is characterized by the constant flow of cold air, visiting during the hot summer months (June to August) is highly recommended. You can enjoy a refreshing stroll through this historical space while feeling the natural chill. However, as the site is located on a slope in a mountainous area, please be mindful of temperature changes and the terrain. Visiting during bright daylight hours makes it easier to observe the intricate details of the stone masonry and the surrounding landscape.
Free guided tours by local commentators are often available (Note: groups must book in advance). Through these tours, you can learn about ancient sericulture techniques and why this specific location was chosen. It is also highly recommended to visit the nearby 'Shimonita Town History Museum'. The museum exhibits materials related to Shunkokan, the organization that managed Arafune Fuka, and documents regarding the Shimonita War, offering a multi-faceted understanding of the region's history.
The area around Arafune Fuka is a beautiful blend of nature and history. The 'Higashidani Fuka' in Nakajo Town is another significant site that adds to the regional historical value. Visiting the Shimonita Town History Museum will allow you to deepen your knowledge of the silk industry that contributed to Japan's modernization. Exploring these spots together provides a three-dimensional view of Japan's industrial history.