Arafune Cold Storage

What to know

The Arafune Cold Storage (荒船風穴, Arafune Fūketsu) was used as a natural refrigerator for the silk industry in the early 1900s. Silkworm eggs were kept cool there to delay hatching, enabling silk production multiple times a year instead of just once. For its role in advancing the silk industry, the cave—along with the Tomioka Silk Mill and one other site—was designated a UNESCO World Heritage site in 2014.

Located in the remote, forested mountains near Tomioka, the Arafune Cold Storage is the largest wind cave in Gunma Prefecture. It could store about a million trays of silkworm eggs for silk producers from across Japan. The cool air inside is generated by wind passing through rock crevices filled with snow that accumulates over winter. Even in summer, when outside temperatures exceed 20°C, the storage remains just a few degrees above freezing.

Originally, three large warehouse-like storage buildings stood atop the wind cave. Each had shelves built into mud-covered walls where silkworm eggs in wooden boxes were stored. These warehouses did not survive, so visitors today can only see the ruined foundations. Guides are on site to provide explanations in Japanese.

If arriving by taxi, you'll be dropped off a short walk from the cold storage. However, if driving, note that the nearest parking lot is quite far—about a 10–15 minute downhill walk along a paved forest road. The road is steep, so the return uphill will take longer (a free shuttle bus runs on weekends). Upon arrival, you can join a short informational tour at no extra cost; explanations are in Japanese only.

The Arafune Cold Storage is deep in the mountains and hard to reach, especially by public transport. It is completely closed from December to March.

From the Tomioka Silk Mill, the cold storage is about an hour's drive on toll-free roads. The last few kilometers are along a narrow, winding mountain road to a free parking lot near Kozu Farm. From there, it's a 10–15 minute downhill walk to the storage; the return is longer due to the steep slope. On short winter days, arrive before 15:00 to avoid walking back in the dark. A closer second parking lot is available 300 meters down the road on weekdays.