The Viharn of Luang Phor Phra Chao Tan Jai is the main assembly hall of the temple, holding immense historical and spiritual significance. It enshrines "Luang Phor Phra Chao Tan Jai," a bronze Lanna-style Buddha image in the Mara Vichaya posture, embodying the serene and bountiful features of the Chiang Saen golden age. The interior is uniquely decorated, blending Rattanakosin and Lanna artistic styles, featuring a golden Prasat-style niche at the rear that serves as a celestial throne for the principal image. The spacious hall is adorned with refined stucco work and murals, reflecting the deep devotion of the Lampang people in creating a sanctuary for a Buddha image believed to grant wishes with miraculous speed.