Nigatsuda Onsen Tonosamayu is a historic hot spring facility with a heritage dating back to the Edo period, located in Nishikata, Ibusuki City, Kagoshima Prefecture. In 1831 (Tenpo 2), the 27th lord of the Satsuma domain, Shimazu Narioki, relocated the Nagai hot spring pavilion to this site, where it served as a therapeutic hot spring resort for successive domain lords. It opened as a public bathhouse in the early Showa period and has been beloved as "Tonosamayu" (Lord's Bath) to this day.

Adjacent to the current hot spring facility lies the "Tonosamayu Ruins," designated as a historical site by Ibusuki City. The original stone flooring, stone-built bathtub, and Western-style tiles from that era are preserved intact, telling the story of the luxury of those times. In the back area, "Yu-gongen" (Hot Spring Deity) is enshrined, and during the Ibusuki Hot Spring Festival's eve celebration, the portable shrine departs from this location.

The current bathhouse has an intimate design, with the bathtub carved with the Shimazu family crest "Maru ni Juji no Moji" (circle with cross), providing a special experience where visitors can enjoy bathing while feeling like lords. Though the bathhouse accommodates only about five people at capacity with its small bathtub, it offers a precious facility where visitors can feel the weight of history and dignity.

Since being transferred to private ownership in 1885 (Meiji 28), the Imabayashi family has managed and operated the facility for three generations, with the current owner being Kazuko Imabayashi, who is over 90 years old. Outside the building, there is a free drinking spring facility using the original water pipes, and visitors can take home the therapeutic spring water, which is believed to be effective for chronic digestive disorders and constipation.