During the past two years we developed a physics game following a unique design principle. Many educational games currently available on the market solely focus on knowledge transfer following a behaviourist principle (Annetta, 2010). The learner is confronted with more or less demanding tasks which are solved using the trial and error method (Skinner, 1938). Learning success is directly assessed using a simple feedback system ("right", "wrong"). Furthermore the audio visual quality of interactive learning software often can't keep up with video games today's target group has become accustomed to. We decided to take a different path. Since fun of play is considered as one of the key elements of an elaborated game playing experience (Vorderer et al., 2004), we decided to design a fun filled and action packed learning game built around a serious topic: renewable energies. The content of the game is based on the physics curriculum while the graphical and audio visual quality of "Ludwig" was designed to stand a comparison with common triple a games. We crafted the game using the powerful open source software Unity. This tool empowered us to create an immersive game environment which was inspired by the look and feel of World of Warcraft. A simple formula "learning goal = game goal" defined the core game mechanics. Based on a constructivist paradigm "Ludwig" offers challenges in an interactive 3d world while learning takes place in an authentic context (McLellan, 1985). Players are allowed to explore the game world, to experiment in virtual laboratories and to solve problems freely while their actions directly lead to consequences and positive feedback by the game. The players actions leave a trace in the game world fostering individual experiences of self-efficacy (Bandura, 1977). Numerous feedback iterations with the target group consisting of students and teachers secured a satisfying level of quality regarding the learning content, the gameplay and the look & feel of "Ludwig". We decided to use an iterative design principle which empowers players to become game designers (Wagner, 2009). By applying qualitative and quantitative methods we gained insights in the applicability of variable quality assurance strategies. Students reflected on the playability of the game, on the usability of the interface and finally on motivational aspects (learning motivation, interest for physics). Teachers reflected on the potential benefits and problems of using "Ludwig" in class. The results of the formative (quality assurance workshops) as well as the summative evaluation (assessment of motivational, cognitive and learning processes) show that "Ludwig" can foster learning processes if game based learning is combined with established teaching methods and material.