Hung King Temple Festival takes place from the 8th to the 11th of the third lunar month in Phu Tho. This festival is held to workship the Hung Kings - who are the founder and the first emperor of the nation. The festival features a procession from the foot of the Nghia Linh Mountain to the High Temple on top of the mountain. Here, there is a ceremony of offering incense of specialities such as chung cakes, day cakes and five-fruit tray to the Kings. There're also many joyful activities including bamboo swings, lion dance, wrestling, xoan singing performances,... In short, I think you should enjoy and do some experience in this festival.