Video games engage players and can train formal skills. However, the potential of educational games for knowledge acquisition lacks research. Moreover, many educational games suffer from low-grade design, therefore impeding the flow of the game and corrupting fun and entertainment.This article describes the "Eduventure II", a research project investigating methods for "subtle" educational game design. Having the thought in mind that subtle embedding of knowledge into a game can preserve its motivational potential, the project team designed and implemented an educational game prototype. This prototype links knowledge to narrative, simulation and game play layers. The here presented text describes the theoretical background, issues, concept and implementation of the prototype, as well as the lessons learnt from a pedagogical perspective.