The park's name refers to 'Saino-kawara,' a mythical purgatory in Japanese Buddhism where children build stone towers, leading to the prevalence of Jizo statues in the area.
The hot spring water here is highly acidic, with a pH level often below 2.0, which naturally disinfects the pools.
The bathhouse located at the end of the park trail covers approximately 500 square meters, allowing it to accommodate over 100 people at once.
The water temperature at the source is naturally very high, requiring cooling processes before it is comfortable for human bathing.
The park features a dedicated 'Onsen Tamago' station where natural steam is used to cook eggs.
Sainokawara Park is a volcanic terrain park in Kusatsu known for its geothermal streams that feed into a massive outdoor mixed-gender hot spring bath. The park is characterized by steaming rock formations and mineral-rich waters that flow through a walking path surrounded by forest. It is the site of the Sainokawara Rotenburo, one of Japan's largest open-air hot springs. The area features numerous small, natural hot spring vents and bubbling puddles resulting from intense geothermal activity. The walking trail connects the Kusatsu town center to the bathing facilities through a scenic valley. As of June 2026, the park remains open to the public, offering year-round access to the forest trails and hot spring amenities. The landscape is dotted with statues related to local folklore, specifically focusing on the theme of 'Jizo' stone deities.
The elevated viewing platform near the park entrance that overlooks the entire steaming valley and forest canopy.
Bring a small towel for the outdoor hot spring, as rentals are available but purchasing can be costly.
Wear slip-on shoes or sandals for easier access if you plan to use the public foot baths located along the park path.
Visit during the early morning or late evening to avoid the peak crowds that gather in the main rotenburo.
Avoid walking off the designated paths, as the geothermal ground can be dangerously hot and unstable.
The main bathing area is mixed-gender, but towels are strictly prohibited inside the water; nudity is the standard requirement.
