The mausoleum at Nikko of Tokugawa, Ieyasu, the first Tokugawa shogun, renowned for the beauty of the shrine and its setting. It was built in richly decorative gongenzukuri style by the Tendai Buddhist monk Tenkai who successfully wrested the authority to enshrine the shogun away from the Yoshida and constructed the shrine in line with Sanno ichijitsu shinto ideas. The main festival is the sennin-gyoretsu (thousand-person procession), a Tokugawa-period costume pageant on May 17-18th. There is a smaller mikoshi procession with 500 participants on October 17th.
A Popular Dictionary of Shinto. Brian Bocking.