First of all, I’m sure you’re wondering what in the world a «fuketsu» is, so let me explain: Fuketsu (風穴) are storage buildings that were traditionally used as natural refrigerators, as temperature inside stays a surprising 8°C (46°F). The secret to keeping these buildings cool is to construct them half way into the steeply slanted slope of a mountain. Due to the large rocks that tend to accumulate on such mountain slopes, cool air is able to flow below the surface of the ground through the openings between the rocks, while warm air is released above ground. Since the fuketsu’s walls are directly in contact with the mountainside, this cool air keeps the air inside the buildings cold as result.
Back in the day, fuketsu were used to store fermented foods such as miso paste and pickles made inekokina, a locally grown leafy green vegetable. During the Meiji Period, they were also used to control the incubation period of silk worms. In fact, the Matsumoto silk producers were the first to discover that this was possible and later the same technique was adopted by other silk producers in Japan.
You can actually go see one of the fuketsu here in Inekoki, a small village in Matsumoto. It is conveniently located a very short walk from the appropriately named «Fuketsu-no-Sato» rest area/souvenir shop (map) that you’ll find on the way to Norikura and Kamikochi. Park your car (or, your tour bus might stop here) at Fuketsu-no-Sato and follow the path over the wooden, arched bridge.
This fuketsu is open to the public so you can go inside and check it out. You’ll see a few photos of how these natural refrigerators are used and be surprised how cold it is even on a hot summer day! Even though it’s open for anyone to walk in, this particular fuketsu is still used today by a few of the local sake breweries to store and age their sake, which you’ll see sitting safely behind a locked, fenced door.
Interestingly, I actually read a newspaper article the other day that talked about how rediscovery of the fuketsu facilities’ excellent ability to age foods and alcohol has spurred others in the Matsumoto area to begin using them again (for example, one person found they were perfect for aging meats!).
For Japanese history buffs, you’ll also be happy to know that the path that runs in front of Inekoki’s fuketsu has a long, long history as well. It was originally part of the Kamakura Kaido (Nomugi Kaido) Road which connected Matsumoto and Hida. In everyday life, it was used by those making pilgrimages to Zenkoji Temple and by couriers using Nagawa oxen to transport goods. Furthermore, the road was used twice by feudal lord Takeda Shingen’s army when they attacked Hida in the mid-1500s!
If you can’t make it for some reason, check out the fuketsu on Google Street View.