We present an approach to geometry learning that is based on play. For a mobile and location-aware game, the concept of smart city learning is exploited to situate learning about geometric shapes in concrete buildings and thus make them more accessible for younger children. A game was developed in close collaboration with a local school and tested on a field trip and in class. A mixed measures evaluation is presented, where the quantitative results show a significant increase in correct answers in a standardized test and the qualitative analysis reveals increased motivation and curiosity for geometric concepts.