It is held over three to seven days during the full moon of the twenty-fifth lunar month (November, but sometimes it is at the end of October) in That Luang – national symbol and most important religious monument of Laos.
The festival starts with a colorful candlelight wax castle (Phasat Pheung) procession which starts the evening before at Vat Simeuang. The procession continues to the next afternoon from Vat Simeuang to Pha That Luang. People carry flowers, candles, incense and wax castles decorated with flowers and bank notes. People wear their best clothes for this procession and there is also a parade of the men and women dressed in various Loa ethnic costumes who dance and play traditional music and songs while approaching the stupa.
The following morning, a huge crowd assembles at dawn at Pha That Luang to give alms to hundreds of monks who come here from around the country, and to play homage to the stupa. In the afternoon, everyone will gather on the esplanade for the traditional game of Ti Khee, which is played with a ball and long curved stick, resembling a game of hockey.
The festival draws to close under a full moon when people from all over Laos will crowd around Pha That Luang for one last candlelight procession. There are also fire work displays to make the end of the celebration. During the Pha That Luang stupa festival, there are trade fairs, concerts and fun fairs held.
According to tourismlaos.org and Wikipedia.