Niji no Yu, the natural hot spring at Tresta Hakusan in Miki Town, is proud of its hilltop location with panoramic views over the town and surrounding mountains. The sauna is a Bona sauna type with heaters installed under the seating and along the back, an uncommon design that reliably warms you from the feet up. With a deep cold plunge bath and a spectacular open-air relaxation area, you can enjoy a blissful totonou (state of perfect relaxation) experience.