Hikiyu at Dake Onsen

The hot springs at Dake Onsen are fed by hikiyu, water piped from sources 1,500 meters up Mt. Tetsu through more than eight kilometers of conduit, one of the longest such systems in Japan. The springs on the mountain produce a combined flow of 1,290 liters per minute at temperatures up to 90 degrees Celsius, arriving at the town at a steady 52 degrees without any reheating needed. This infrastructure dates to 1824, when the original mountain-side resort was destroyed by a landslide and Nihonmatsu domain rebuilt the facilities downhill using the same pipe-engineering knowledge they had developed for the castle's water supply. PVC pipes replaced hand-drilled pine logs starting in the 1950s.