Seiganto-ji is a Buddhist temple located in the Wakayama Prefecture of Japan, near the base of the Nachi Falls. The temple is part of a UNESCO World Heritage Site known as the "Sacred Sites and Pilgrimage Routes in the Kii Mountain Range".

The temple is believed to have been founded in the 4th century, making it one of the oldest temples in Japan. It was initially a Shinto shrine before being converted to a Buddhist temple by the monk Ragyō Shōnin.

The temple complex includes a number of buildings, the most notable of which is the Nachi Taisha Grand Shrine. This shrine is dedicated to the kami (god) of waterfalls and is one of the three Kumano Sanzan shrines in the area. The shrine is built in the traditional Japanese architectural style and has a distinctive red-painted exterior.

Another important building at Seiganto-ji is the Seiganto-ji Pagoda, which is located beside the Nachi Taisha Grand Shrine. The pagoda is a three-story wooden structure that stands 30 meters (98 feet) tall. It is a National Treasure of Japan and is one of the most photographed landmarks in the country.

Seiganto-ji is also known for its connection to the Kumano Kodo, a network of ancient pilgrimage trails that connect various Shinto and Buddhist sites in the Kii Mountains. The temple served as a starting point for many of the pilgrims who journeyed along the Kumano Kodo in ancient times.