This giant open-air bath is created by damming the Ohtou River and letting the natural hot spring waters fill the pit. Because much depends on Mother Nature, the pool tends to be a different size every year. The water springs from the riverbed at a hot 73 degree but then mixes with the crystal clear waters of Ohtou River, bringing the temperature down to about 40 degree. The pool is enclosed along the perimeter by a reed screen, leaving the rest open to the skies and stars for you to enjoy while soaking in the warm waters.
| Location | Kawayu Onsen (Ohtou River) |
| Period | December thru February |
| Bathing time | 6:30 a.m. – 10:00 p.m. (locked at 10:00 p.m. ) |
| Parking | About 50 cars (200 meters downstream from the bath) |
- Please refrain from bringing glass objects.
- On rainy days the bath may be closed.
- No pets allowed.
- No shampoo or soap allowed.
- Please keep area clean.