The Grand Marché of Ouahigouya is the commercial and social heart of the city, spread across a wide area near the center of town. The market is most animated on the weekly market day, when traders come in from surrounding villages and even from across the Mali border — bringing livestock, grain, cloth, and goods that you won't find in the permanent stalls.
On ordinary days, the permanent sections sell food staples, hardware, clothing, and the kind of plastic goods that fill markets across West Africa. The cloth section is worth seeking out: Mossi weavers produce distinctive striped cotton fabric, and you can watch it being made and buy lengths directly. The market has a matter-of-fact quality — this is not a tourist market but a working one, and the transaction of daily life around you is genuinely interesting to observe.