The local appropriation of the Taoist Nine Emperor Gods Festival, it is a Thai-Chinese religious festival of nine—or ten, for some oldtimers—days during which festival devotees refrain from eating all kinds of meats and by-products, avoid sins, and, if possible, visit Chinese shrines to offer prayers.
The best place to observe the Thai Vegetarian Festival is the city's Chinatown, Yaowarat.
Check out our list of best vegetarian restaurants in Bangkok here.