Obesity is a growing problem among children, due in part to their sedentary lifestyles. Time spent engaged in physical activity is decreasing, while time spent playing computer and video games is on the rise. We leverage children's interest in digital games to encourage families to engage in purposeful walking. We present a GPS-based game, played on a mobile device that uses walking as a primary gameplay mechanic. Our game, PiNiZoRo, includes a fighting game, triggered at points along a real-world route, and a map editor that allows parents and recreation specialists to create custom routes in their neighbourhoods. Results from an initial focus group with parents were positive, as they showed enthusiasm for the concept, implementation, and gameplay.