Location-based games can engage visitors of a cultural site in learning and sensitization activities about local heritage. This paper reflects on the design thinking approach followed to develop a mobile learning game about the cultural heritage (CH) of industrial oil production in Lesvos Island, Greece. The game starts in the museum and continues in the settlement, where users (players) are presented with location-based learning missions and challenges about tangible and intangible CH. Empathy about this project was sparked with field visits in the museum and the settlement that increased team motivation and established several cooperation practices among members and local experts. Definition of the problem focused on system architecture. Ideation involved several iterations of the core team about focused design issues and a few larger in-scope iterations of the whole project team. The design of the mobile game emphasizes exploratory learning and storytelling including digital characters and narratives, as well as rewards in augmented reality (AR), where users view traditional tools in 3D. Prototyping involved technical experimentations, lab, and field prototypes. Testing was an empirical process that gradually developed from inspections to field playtesting involving both local experts and visitors. We reflect on lessons learned about the design thinking process, re-iterating on important principles and guidelines for cultural heritage projects.