The Arafune Cold Storage (荒船風穴, Arafune Fūketsu) served as a natural refrigerator for the silk industry during the early 1900s. Silkworm eggs were chilled there to prevent them from hatching, allowing silk production to be carried out multiple times per year instead of just once. In recognition of its contribution towards the advancement of the silk industry, the Arafune Cold Storage is one of three sites alongside the Tomioka Silk Mill that attained world heritage status 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 in the storage is produced by wind passing through rock crevices filled with snow accumulated over winter. Even in the summer when the outside temperature is over 20 degrees Celsius, the temperature in the cold storage remains just a couple degrees above freezing.
In the past, three large warehouse-like storage facilities stood on top of the wind cave. Each featured shelves built into the mud covered walls where silkworm eggs, placed into wooden boxes, could be stored. Unfortunately, these warehouses did not stand the test of time, and visitors to Arafune Cold Storage can currently only see the facilities' ruined foundations. Guides are present at the site to provide visitors with explanations in Japanese.
If arriving by shuttle bus or taxi, visitors will be dropped off just a short walk away from the Arafune Cold Storage. However, visitors arriving by car note that the closest parking lot is located rather far away from the storage. It is about a 10-15 minute walk downhill along a paved road through the forest from the parking lot to the storage; and since the road is rather steep, the ascent back to the parking lot is likely to take considerably longer.
The Arafune Cold Storage is located deep in the mountains and difficult to access, especially if you travel by public transportation. It cannot be accessed, at all, during the winter from December to March.
From the Tomioka Silk Mill, the Arafune Cold Storage can be reached in about one hour by toll-free roads. The last few kilometers are along a narrow and winding mountain road to a free parking lot not far from the Kozu Farm. From the parking lot, it is a 10-15 minute downhill walk to the cold storage. Walking back to the parking lot is likely to take longer due to the steep terrain. During days with shorter daylight hours, visitors are encouraged to arrive before 15:00 to avoid walking back to the parking lot in the dark.
Shimonita Station, the terminal stop of the Joshin Railway, is the closest train station to the Arafune Cold Storage. It can be reached in about one hour from Takasaki Station (1110 yen one way). However, from the station it is still over 15 kilometers to the cold storage:
On weekends, take a bus from Shimonita Station to the Sun Sports Land (about 30 minutes, 200 yen one way) from where there is a free shuttle bus to the Arafune Cold Storage (about 20 minutes). Note, however, that there are only two connections per day. The bus stops just a short walk away from the cold storage.
On weekdays, the Arafune Cold Storage cannot be reached by public transportation. Instead, visitors should hire a taxi or "sightseeing taxi" from Shimonita Station. "Sightseeing taxis" are considerably cheaper than regular taxis, but require advance reservations. The most basic package for a sightseeing taxi to the cold storage and back costs around 4000 yen.