Storage unique to snowy regions uses ice houses or snow cabins. Ice houses are used in Niigata, Ishikawa and Nagano, etc., while snow cabins are used in Niigata, Yamagata and Akita, etc. The ice and snow which do not melt even in summer make the room temperature approximately 1-5 degrees C. There, even in summer you will get cold if you are wearing only a T-shirt, but this environment enables sake to be matured slowly over time.
Lastly, the most surprising storage place would be an air-raid shelter. As places available for the shelters are limited, you can guess the specific sake from the place of shelters. However, the shelters are convenient because they are within the premise of breweries. Though they are not made deep under the ground, in the mountains or in the woods, it is cooler than you would expect.
These types of storage have an advantage of being vibrationless, which makes sake matured quietly and slowly without any stress.