One of the most impressive temples in the old city, Wat Chedi Luang centres on a huge brick chedi that dates back to the 14th century. The structure originally stood around 80 metres tall before an earthquake brought down the upper section in 1545. Even in its partially ruined state, the chedi is massive and atmospheric, especially when lit up at night.
The compound is active — monks live and study here, and there's a casual "Monk Chat" programme where visitors can sit with novice monks and talk about Buddhism, Thai culture, or whatever comes up. The City Pillar Shrine (Lak Mueang) sits under a large gum tree in the grounds, considered the spiritual centre of Chiang Mai. Free to enter, though donations are welcome.