Kad Nan (also written as Kat Nan) is a street (and square) in Nan city (opposite the fire department) that started out as a kind of open-air shopping mall. With small shops and some coffee shops. And although some places are indeed still open in day-time Kad Nan is best visited in the evening. Actually it is one of Nan's let's say entertainment streets, but then in an upcountry low-profile way. A great street to visit Coffee Shops, Restaurants and Pubs. Nice (not too loud) live music, friendly atmosphere and good food. I love it! A street to visit when you are in Nan. For more information about Nan province see Destination Travel Guide Nan province, North Thailand.
Update 2018 : I looks like that the last days of Kad Nan are numbered as some shops have move out / closed and on another street nearby they are making a kind of new Kad Nan.
Update 2020 : I looks like all shops are closed and the all place is being renovated.