Wat Phra Si Rattana Mahathat — everyone calls it Wat Yai, meaning simply the Big Temple — is Phitsanulok's great reason to visit, and one of the most important Buddhist sites in Thailand. The temple was founded in 1357, and its centrepiece, the Phra Phuttha Chinnarat, is considered by many Thais to be the most beautiful Buddha image in the country. Tens of thousands of people make pilgrimages here every year, and the atmosphere around the image — lit by oil lamps, framed by flame-like golden halo — is genuinely powerful.
The image sits in the main wihan, a tall gilded chamber that has been expanded and rebuilt over centuries. The best time to visit is late afternoon, when the slanted light coming through the windows falls directly on the bronze. Outside, the temple compound contains a smaller museum with objects from the site and a busy market of religious goods and Buddha amulets.
The temple is on the east bank of the Nan River, just south of the Naresuan Bridge. Entry is free; modest dress is required. The compound is open from early morning until around 9pm.