Being a former French hill station, it is situated in the midst of mountains, just south of the Fansipan, with 3143 m the highest point of Vietnam. Especially the Hmong sell beautifully embroidered bags, caps, jackets, etc.
Market day is every day, but the weekend is special.
But the weekend is also specially crowded with foreigners, so it's probably a good idea to avoid it. I dare say that someone who has been there just one year ago will not recognize it anymore and certainly not like the crowds. A wonderful place. The surroundings are breathtaking, and the atmosphere friendly. Sa Pa. They wear their beatiful costumes, and they would wear them even if the tourists weren't there, which felt good.