Escape into the forest for a truly unforgettable soak at this expansive open-air hot spring, nestled along a serene mountain stream. You'll feel completely immersed in nature as you relax in the strongly acidic, sulfurous waters, famed for their skin-beautifying properties and known locally as the "Princess Water." The baths are built from natural stone, large enough to share with 200 others, creating a unique communal yet peaceful experience. Just be aware, this is a traditional, rustic onsen, so there are no showers or modern facilities, allowing for an authentic connection with the centuries-old bathing culture of Zao.