A municipal public bathhouse located in the central downtown area of Yamaga City, Kumamoto Prefecture, serving as the original source bath (motoyu) of Yamaga Onsen, a hot spring town whose history dates back to the Heian period. The bathhouse traces its origins to 1640 when Hosokawa Tadatoshi, the first lord of the Higo Hosokawa domain, established it as a clan tea house, with records in the Hosokawa domain archives noting that the legendary swordsman Miyamoto Musashi was invited to its completion ceremony. After being demolished in 1973, the bathhouse was faithfully reconstructed in 2012 using traditional Japanese carpentry techniques as the largest wooden hot spring structure in Kyushu. The spring is an alkaline simple hot spring with a pH of 9.62 and a source temperature of about 40 degrees Celsius, supplied as free-flowing source water (gensen kakenagashi). Its silky, lotion-like texture, abundant flow of 500 to 600 liters per minute, and reputed benefits for neuralgia, muscle pain, fatigue recovery, chronic digestive issues, and poor circulation make it one of the most beloved hot springs in Kyushu.