Busshozan Onsen Tenpyoyu is a day-trip hot spring facility located in the historic temple town of Busshozan in southern Takamatsu City, Kagawa Prefecture. Drilling began in 2002 and the facility opened in 2005. The spring source, named 'Busshozan Sunamushi Onsen,' yields a sodium bicarbonate-chloride spring (weakly alkaline, high-concentration, low-temperature hot spring) with a pH of 7.5, source temperature of 32.6°C, and total mineral content of 10,847.8 mg/kg. Rich in sodium (3,322 mg), bicarbonate (5,259 mg), and chloride (1,809 mg) ions, the water produces a silky-smooth feel that has earned it a reputation as a 'beauty spring.' The building was designed by Takamatsu-born architect Shohei Oka and received the Good Design Award in 2007 for its sophisticated modern aesthetic. The facility features outdoor baths (three pools made of Japanese cypress, hinoki cypress, and stone) arranged around a central courtyard, plus indoor baths, all of which operate as flow-through spring water. Unique cultural amenities include window-side tatami seating along the corridors and a secondhand bookshop called 'Busshozan Bunko' where visitors can browse or purchase books to read while soaking. The town of Busshozan flourished as a temple gate district since the Edo period, home to the Matsudaira clan's family temple Honen-ji, and the hot spring facility is designed to harmonize with this rich historical townscape.