Chatuchak Weekend Market is the largest outdoor market in Thailand maybe even worldwide,covering a total area of 35 acres. Thousand of small stalls and shops selling furniture,food,art,food,clothing items & accessories,pets,food,souvenirs,food,plants and more food lol. Buy a map at the start, makes it easy to get round. Bargaining is expected, but the prices are generally much cheaper than at the regular shopping venues. A big clock tower in the centre makes it feel like a maze. Spectacular !!
p.s. there are a lot of Markets in Bangkok: Pratunam Market, Suan Lum Night Bazaar, Patpong Night Market, Taling Chan Floating Market, Khao San Road, Banglamphu Market, and probably a few more as well.