Iwanesawa Sanjinja stands in the Iwanesawa hamlet of Nishikawa Town. 

Its origins date to 1226, when a traveling monk from Yamato Province paused in the secluded valley of Iwanesawa. According to tradition, his stay gave rise to a small devotional structure, marking the site as spiritually significant. Linked to the spiritual legacy of En no Gyoja, the founding figure of Shugendo, the site soon became a starting point for ascetic practice, and a route was opened toward Mt. Gassan. Over time, Iwanesawa developed into an important gateway for mountain worship, drawing generations of practitioners.

In 1387, a large temple complex was established, formalizing the site’s role within the Tendai Buddhist tradition and connecting it to wider religious networks. The temple was administered by clergy appointed from Toeizan, ensuring continuity of ritual knowledge and institutional ties beyond the region.

The complex was repeatedly rebuilt in 1667, 1744, and 1841, reflecting both the severity of the mountain environment and the determination of local religious communities to sustain the site. Recurrent fires placed lasting constraints on resources, and the main entrance was completed only in 1858. These cycles of destruction and renewal form an integral part of the site’s historical character.

Everyday life and religious practice were closely intertwined. This is symbolized by the life-size wooden statues of Daikoku and Ebisu enshrined within the kitchen’s octagonal pillar, emphasizing the spiritual significance of food, labor, and communal life in mountain temples.

In 1869, following the national policy separating Shinto and Buddhism, the temple relinquished the name Nichigetsu-ji. In recognition of its cultural, historical, and spiritual significance, Iwanesawa Sanjinja was designated an Important Cultural Property of Japan in 2000.