🗺️ Yukawa Onsen (玉川温泉)

Yukawa Onsen has a pH value (indicating hydrogen ion concentration, acidity) of 1.2, making it the most acidic hot spring in Japan, widely known as a "therapeutic and restorative bath." It features a spring outlet known as "O-sen" that gushes forth water at a temperature of 98 degrees Celsius, with a flow rate of 9,000 liters per minute, far surpassing other hot springs in scale. The water quality is characterized by a sulfurous scent and radium, possessing high antibacterial properties and being colorless and transparent with strong acidity. There is even a saying that a kitchen knife left soaking in the spring overnight will dissolve. Almost all bathing areas use water that is less than 50% from the source (though some use 100%). The air is also filled with acidic steam, which can tarnish precious metal jewelry and potentially cause malfunctions in precision devices like smartphones, so special care is advised. Additionally, Yukawa Onsen is a source of the radioactive mineral "Kito stone," which releases trace amounts of radium. Visitors can also enjoy warm baths like rock baths while lying on laid-out grass mats. Yukawa Onsen is a standalone accommodation that exudes a strong traditional onsen atmosphere. For those who may not be able to accept this, it is recommended to visit the sister facility "Shin-Yukawa Onsen," which uses the same source but is equipped with modern amenities.

Japan's number one strong acidic hot spring. The outflow from a single source is also the highest in Japan. This hot spring primarily focuses on therapeutic bathing, which may give it a hospital-like atmosphere. Almost all guest rooms have a simple structure without bathrooms, televisions, or refrigerators. You can enjoy natural rock baths in the area near the nature research trail by the rock formations. Due to the acidic spring water that can dissolve iron, please follow the bathing instructions and do not overdo it.