Onsen-ji, Buddhist temple in Arima Onsen, Japan

Onsen-ji is a Buddhist temple with buildings positioned across a forested mountainside, including a Yakushi Buddha hall located at the lower level near the Kono-yu bath house. The structures are arranged across the grounds, forming a cluster of temple buildings that integrate with the natural landscape.

According to temple tradition, Gyōki founded Onsen-ji in 724 on the slope of Mount Atago after Yakushi Nyorai told him to revive Arima's declining springs. A flood destroyed it in 1097, and the monk Ninshō rebuilt it in 1191, establishing twelve lodgings named for the twelve divine generals who serve Yakushi. The main hall burned in 1576 and again later; the present Yakushi-dō dates from 1781, after early Meiji anti-Buddhist measures abolished the Shingon temple and left only this hall.

The temple's name links it to Arima's hot springs: its formal name is Arima-san Onsen Zenji. The grounds hold two Kamakura-period gorintō stupas, one attributed to Taira no Kiyomori and one to Jishinbō Son'e, both Kobe City designated cultural properties. The Misoshi-an hall displays statues of Gyōki and Nisshin. Annual rites are the Nyūsho-shiki on 2 January and the Misoshi-matsuri on 14 November.

Onsen-ji stands at 1643 Arima-cho, Kita-ku, Kobe, a six-minute walk from Arima Onsen Station on the Kobe Electric Railway and about ten minutes from the Rokko-Arima Ropeway station. The Yakushi Hall sits on the slope of Mount Atago in the Rokko range, so the approach involves climbing; the temple is stop 3 on the Arima-gun Saigoku Kannon pilgrimage.

The temple's full name is Arima-san Onsen Zenji, and it belongs to the Obaku school even though it began as a Shingon temple. Its founder is remembered in the Misoshian hall, a small museum where statues of Gyoki and the monk Ninshi are kept alongside documents on the temple's history.