I use the mall too. But it shouldn't be your only exercise. It was for me but the problem was I got plantar fascitis AND I got so conditioned to it that i wasn't losing the weight as well walking. Use other exercises too if you can and switch off. As far as walking goes, my walking includes indoor walking at the mall, outdoor walking at Georgia's state parks (there's one near me), and aggressive walking on LA Fitness's treadmills. You want the variation in altitude that outdoor walking and treadmills can give you.