Nitta-no-Yu is one of the three public bathhouses in Kakuma Onsen, located in Yamanouchi Town, Nagano Prefecture. Kakuma Onsen is a historic therapeutic hot spring village said to have been discovered by Rennyo Shonin, a high priest of Jodo Shinshu Buddhism, during the Muromachi period. The area has been beloved by many literary figures including Fumiko Hayashi, Eiji Yoshikawa, and Taikan Yokoyama. The distinctive feature of Nitta-no-Yu is its use of blended water from two sources: Yakushi-no-Yu and Miroku-no-Yu. The bathtub is known for its beautiful deep indigo color that sparkles like stars, with black mineral deposits (yu-no-hana) dancing in the clear water. The exterior is an atmospheric old wooden building with high ceilings and antique wooden hot spring analysis boards that evoke traditional hot spring charm. The spring water is a sodium-chloride and sulfate hot spring. While cold water is added to achieve a suitable bathing temperature, the water is fresh without heating, circulation, or disinfection. The temperature tends to be quite hot. Access requires a special wooden key (marked Kakuma-gumi) borrowed from the accommodation. Since the closure of Kurotori Store, which managed the keys, at the end of 2019, access is now limited to guests staying at Kakuma Onsen ryokans. The spring is said to be effective for arteriosclerosis, cuts, burns, and skin conditions.