High in the mountains of southwestern Gunma, near the border with Nagano, a series of stone-walled pits sit among the trees on a hillside. They look like ruins, and in a sense they are, but in their day they were cutting-edge technology. The Arafune cold storage, built in the early twentieth century, used the cold air flowing out of crevices in a rocky slope, a natural wind cave or fuketsu, to keep silkworm eggs cool and delay their hatching. This allowed silk farmers to raise several batches of silkworms a year instead of just one, greatly increasing production. At its peak, the facility stored eggs for farmers from across Japan and even abroad. It is part of the UNESCO listing of the Tomioka Silk Mill and Related Sites, inscribed in 2014, which tells the story of how Japan became the world's largest exporter of raw silk.
The Tomioka Silk Mill itself, founded by the Meiji government in 1872 with French engineers and machinery, stands in the town of Tomioka, about twenty-five kilometres away, a huge complex of brick buildings that remained in operation until 1987. Together with the cold storage and two sericulture farms, it shows the whole chain of silk production, from egg to thread.
The cold storage is in the town of Shimonita, famous throughout Japan for two products: konnyaku, a jelly made from the corm of the devil's tongue plant, and Shimonita negi, thick, sweet leeks that are prized in winter hot pots. Roadside shops sell both, and konnyaku dishes appear on every menu.
The riding is mountainous and beautiful. Route 254 climbs from Shimonita through forests to the Uchiyama pass and descends into the Saku basin in Nagano, with tight bends and views over the ridges. The roads around Arafune itself are narrow and steep, with a final access road to the site that requires care. The Myōgi mountains, a range of jagged volcanic peaks, rise to the east, with a famous winding road along their flanks. The surface is excellent, traffic light, and the scenery superb, especially in autumn, when the maples turn red.
Shimonita and Tomioka have fuel and convenience stores, and Saku has more services on the Nagano side. The site sits at high altitude and is cold even in summer, which was precisely the point; bring a layer.