My rating:
Up on a hill at the northwest corner of town is the old temple of Wat Phrathat Doi Tong. The temple was supposedly started by the Prince of Chiang Rai in 940. Its golden chedi (pagoda) is visible from far away when approaching the city from the north.
The pagoda and main chapel of Wat Phrathat Doi Tong
The wiharn (chapel) appears quite modern and is not very interesting. The exterior is not very fancy as Thai temples go. Inside, the hall is decorated in the red and gold typical of northern temples. There are some nice contemporary murals on the wall.
A Chinese shrine just below the Thai temple
A short way down the north side of the hill, a Chinese shrine backs into the hillside under the temple. The red-and-gold sign on the porch of the shrine curiously reads (in thai) "Hall [of] the godfather [of] Doi Tong." Yes, "godfather" is the correct common translation of the Thai. There's a good view north of Chiang Rai from the shrine, and a stairway leads down to the road that can take you across the Kok River.
At the very peak of the hill, just south of the temple grounds, is the new City Pillar which was erected in 1988.