The Phra Ruang Castle Mound is located to the east, adjacent to Wat Mahathat. It is believed that this area once served as a royal castle foundation for the kings of Sukhothai. In 1983, the Fine Arts Department conducted excavation and restoration work. They discovered the foundation of a structure designed with an inverted lotus base and an upright lotus base, characterized by a high rectangular platform measuring 27.50 by 51.50 meters, with staircases at both the front and back.