Wat Phra Si Rattana Mahathat, also known as Wat Yai, is a Buddhist temple located in Phitsanulok Province, Thailand. Founded in 1357 by King Lithai of Sukhothai, the temple is famous for its stunning golden Buddha statue called Phra Phuttha Chinnarat. The temple's large vihara features intricate mother-of-pearl inserts donated by King Boromakot in 1756, and a Khmer-style prang said to enshrine relics of the Buddha. Visitors can also explore the Phuttha Chinnarat National Museum on the temple grounds, which showcases ancient artifacts and art objects reflecting the history and culture of Phitsanulok and its surroundings. Festivals and events, such as the annual Phra Phuttha Chinnarat Fair, are held on the temple grounds, making it a vibrant hub of cultural and religious activities in the region.