What is the Shinto ritual of rebuilding Ise Grand Shrine every 20 years called?

The Shinto ritual of rebuilding Ise Grand Shrine every 20 years is called Shikinen Sengū.

Shikinen Sengū is the periodic reconstruction and transfer ceremony at Ise Jingū, Japan’s most important Shinto shrine complex. The principal sanctuaries of Naikū, dedicated to Amaterasu, and Gekū, dedicated to Toyouke-Ōmikami, are rebuilt on adjoining sites. The kami’s sacred objects are then transferred to the new buildings.

The practice is associated with tokowaka, the ideal of continual renewal. Rebuilding keeps the shrine ritually fresh, preserves its distinctive ancient architectural style, and passes carpentry and craft knowledge from one generation to the next. The ceremony is therefore both religious observance and cultural transmission.

Although described as a 20-year cycle, each reconstruction project takes many years of planning, preparation, timber work, and construction. The tradition dates to the late seventh century, with the first recorded Ise reconstruction commonly dated to 690 CE. Wars and other disruptions have occasionally delayed the schedule.

Shikinen Sengū should not be confused with Niiname-no-Matsuri, a harvest thanksgiving, or Daijōsai, the emperor’s accession harvest rite. “Sengū” refers to transferring the deity to a new shrine building.