Plunder Planet is a dynamically adaptive fitness game environment which was developed with and for children and young adolescents. It takes the player on a rapid treasure hunt on a desert planet. The exergame provides a holistic, motivating and effective training experience. Unlike commercially available exergames, Plunder Planet can be controlled with two different motion-based controllers demanding either haptic or gesture-based input movements. Additionally, the player is guided towards his/her individual perfect training mode by specific game mechanics. Based on the player’s heart rate and in-game performance the game difficulty and complexity are continuously adjusted to the physical and emotional states and needs of the player during the training session. The game was developed in an iterative and user-centred design process by a sports scientist and a team of game designers. The R&D-project is located within the Subject Area Game Design of the Zurich University of the Arts.