The biggest market in Chiang Mai is the Muang mai market.
It is here the majority of the northern hill tribe farmers sell the fruits and vegetables they grow in the mountains.
It is both a normal market and a whole sale market. It is mainly fruit and vegetables witch are sold here, but you will also find meat and fish.
Beside this, it is as well buyers from Bangkok and other parts of Thailand who are buying fruit and vegetables, and you see many cars packed with fruit and vegetables that will be sent to the southern provinces.
The market cover an area of several streets and side streets. This area have many warehouses as well. Farmers park their pick ups filled with fruit and vegetables inside the ware houses and are selling directly form the cars.
In the evening, the farmers who have no permanet stand in the market, are setting up shop at the sidewalks. Chiang Mai Muang Mai market are becoming a real tourist attraction. Over the last few years i have seen more and more big tour busses with Chinese tourist visiting the market.
I can really recommend a visit to the market, both because it is very picturesque, and because it shows what are grown in the mountains north of Chiang Mai.