Arafune Cold Storage

Arafune Cold Storage (荒船風穴, Arafune Fūketsu) is a remarkable natural cave nestled in the forested mountains of Gunma, once a key element in Japan’s silk industry. In the early 1900s, it served as a vital facility for silk producers, who used the cave’s naturally cool air to store millions of silkworm eggs. Cold air from underground rock crevices, filled with winter snow, flowed into the cave, keeping the eggs at a low temperature and preventing them from hatching too early. This innovative method allowed silk producers to harvest silk multiple times a year. Even in the peak of summer, the cave's temperature remains just above freezing, preserving the eggs in optimal conditions.

The cave, along with the Tomioka Silk Mill, was designated as a UNESCO World Heritage site in 2014, recognizing its historical significance to Japan's silk industry. Visitors can explore the foundations of old storage buildings and learn more about the cave’s role in silk production through brief on-site tours, available in Japanese. To reach the cave, visitors must take a 10–15 minute downhill walk through the forest from the parking area, or they can take a free shuttle bus on weekends. Taxis are available for a closer drop-off, offering more convenient access to the site.