Shirako Onsen Tokaiso

Shirako Onsen Tokaiso is a hot spring inn located in Nakazato, Shirako, Chosei District, in the southern part of the Kujukuri coast in Chiba Prefecture. Shirako Onsen is a relatively young hot spring area, developed in 1989 after a 2,000-meter exploratory well was drilled. Tokaiso is one of the inns drawing on this source and also welcomes day-trip bathers. According to local legend passed down at nearby Shirako Shrine, a white snake was once seen coiled atop a white turtle that drifted ashore from the sea, a story tied to the town's name and folk beliefs, distinct from the geological origin of the hot spring itself.

The water is classified as a sodium chloride spring (from well No. H-106), notable nationwide for its high iodine content. It has a pH of 7.5, a source temperature of 28 degrees Celsius, and a total mineral content of 33,113 mg/kg. The bath water ranges from amber to oolong-tea brown, with a distinctive iodine scent and a strongly salty taste. Because the source temperature is close to body temperature, the water is both diluted and heated before use, and treated with chlorine disinfection and circulation filtration rather than being supplied directly from the source (kake-nagashi). Multiple wells exist in the area, and treatment methods may differ slightly between inns.

The bathing facility consists of separate indoor baths for men and women only; there is no open-air bath. Day-trip bathing costs 600 yen for adults and is available from 12:30 to 17:30 (not available on Saturdays; closed December 30 to January 3). Free parking is available for about 30 cars on a first-come basis. The 33-room inn offers room-only stays starting from 5,500 yen (excluding tax).