Phrathat Yakhu or Phrathat Yai is the largest chedi in Fa Daet Song Yang. It is an octagonal-shaped chedi, made of bricks. Evidence shows that it was constructed for three periods. The pedestal was in a redented square shape, with staircases at the four directions and decorated with stucco built during the Dvaravati period.
The upper pedestal was in an octagonal shape, built on top of the original one and supporting an old chedi of the Ayutthaya period. The body and the top were created in the Rattanakosin period. Around the Phrathat, there are boundary stones with bas-reliefs depicting the life of the Lord Buddha. For this Phrathat, local people believe that it stores the bones of a respected senior monk.
It can be noticed that when Mueang Chiang Som won the battle, they destroyed everything in Fa Daet Song Yang, except for Phrathat Yakhu. For this reason, the remains of the Phrathat are still in perfect condition. In the month of May every year, there will be the annual Rocket Festival, which is the ceremony to ask for rain to make the village live in peace.