Katsura no Yu is a municipal public rock bath located along the Shiroishi River in Shiroishi City, Miyagi Prefecture. Obara Onsen was reportedly discovered by Hitachibou Kaison, a retainer of Minamoto no Yoshitsune, at the end of the Heian period, making it a historic hot spring area. It has long been known as 'Me ni Obara' (Obara for the eyes), renowned for its effectiveness in treating eye ailments. Katsura no Yu is a rustic rock bath built beneath a massive rock overhang with a simple roof, creating a unique cave-like bathing atmosphere. The source is called 'Me no Yu' (Eye Spring), and the water is a simple hot spring (low osmotic pressure, weakly alkaline, high temperature spring) with pH 7.9, a source temperature of 53.2 degrees Celsius, flowing naturally without circulation. Located near the entrance to the Hekigyokukei gorge walking trail along the Shiroishi River, bathing while listening to the river is a truly special experience. Soap and shampoo are prohibited as there is no sewage system, which helps preserve the natural spring environment. The admission fee is just 200 yen, making it remarkably affordable and beloved by locals and hot spring enthusiasts. There are separate rock baths for men and women, each accommodating about six bathers with one washing station.