The Treasury Museum Chiang Mai is a small government-run museum in a heritage building in the old city. Its focus is money, taxation, and treasury work in northern Thailand, which sounds dry until you start seeing how coins, banknotes, and official objects tie into Lanna history.
It is not a blockbuster museum, but it is a useful one-hour stop if you are already around Wat Chedi Luang or the Lanna Folklife Museum. Shoes come off before entering, as in many Thai historic interiors.