Officially called Rengeo-in, it is an ancient temple of the Tendai sect. The main hall, rebuilt in the Kamakura period, is a long hall stretching about 120 meters from north to south and is designated as a national treasure. All of the Buddhas enshrined there, including the principal image, the Thousand-Armed Kannon Seated Statue, and the 1,000 Thousand-Armed Kannon Standing Statues , are national treasures.

In commemoration of the designation of all Thousand-Armed Kannon Standing Statues as national treasures in 2018, the statues that had been entrusted to the National Museum were returned to the main hall, bringing the total number of statues to 1,001.

In the same year, the arrangement of the 28 Buddhist Guardian Deities and the wind and thunder god statues was returned to their original state based on Kamakura period woodblock prints and previous academic research. In addition, the grounds include a stroll-style garden with a pond, which was developed in 2021, as well as the Great South Gate and Taiko Wall, which were built in the Momoyama period, and are designated as Important Cultural Properties.

Emperor Goshirakawa ascended to the throne as the 77th Emperor in 1155, and after only three years he abdicated to Emperor Nijō, after which he ruled as a retired emperor. Sanjusangendo was built in his palace in 1164, but burned down 80 years later and was soon rebuilt by the retired emperor Gosaga.

It continued to be well looked after and was fully restored by Yoshinori, the sixth Ashikaga shogun of the Muromachi period. He entered the Buddhist priesthood and served as the head priest of Tendai-ji Temple at Mount Hiei, ordering donations to be made to Zen temples in Kyoto for repairs, and carrying out maintenance both inside and out, including replacing roof tiles and renovating central statues and thousand Buddha statues.

At the time, this area was a key transportation point, and Hideyoshi wanted to emulate the prosperity of Emperor Goshirakawa and Kiyomori. To demonstrate his power to the nation, he built the Great Buddha Hall of Hokoji Temple, modeled after the Great Buddha of Nara, to the north of Sanjusangendo. He also built an earthen wall around the temple and the tomb of Emperor Goshirakawa. The remains of this structure, the Great South Gate and Taikobei Walls (both designated Important Cultural Properties), remain to this day.

Repairs to the temple were also carried out meticulously, including the installation of a thousand Buddha statues, and continued until the time of Hideyori, who succeeded Hideyoshi. The Great Buddha Hall was completed in September 1595, and a memorial service was held to celebrate its completion by a thousand monks. After

his death, Hideyoshi was deified as Toyokuni Daimyojin, and a magnificent shrine was built on Amigamine, to the east of the temple.