Tucson and the Southwest might not come to mind when you think about walkability. Sunbelt cities are famous for their devotion to the automobile. Consequently, an avid walker might balk at the idea of a walkable city in Southern Arizona. No doubt the choices are limited compared to the older, denser, more dynamic cities of the East Coast or Europe.
It often strikes me how different modes of travel affect my experience of a place. Walking down a street for the first time after having driven the same street countless times opens up an entirely new world. This is valuable to keep in mind when making travel plans, too. If you really want to experience a place fully, how you go is as important as where you go.