The location-based smartphone game Stadtflucht (German for urban flight or city escape) is an explorative prototype conceived as a research tool to analyze the perception of urban space. Our overall research on game experiences aims to foster active recreation in urban environments, facilitate the assessment of users' perception, and encourage their participation in urban planning processes. This article assesses how the prototype was able to engage participants in a playful manner with the built environment in a study in Frankfurt am Main, Germany. First, we introduce location-based games as a suitable research tool to achieve this type of playful interaction. We then present the theoretical frame-work for the use of smartphone technology to record behavioral data and measurements of physiological reactions used in the prototype. Finally, we outline a set of tasks that support interaction with the built environment and conclude with observations and suggestions for future research.