We developed an exciting location-based, mobile game that allows first year students to explore the university campus in the fashion of a paper chase game. The players try to find virtual, geo-referenced riddles, located at different interesting spots. When approaching such a spot the corresponding multimedia riddle is displayed and the player tries to solve it. To support the player's
orientation and navigation, we developed a multimodal user interface. On the one hand the checkpoints and current position are shown on a geo-referenced graphical map. Alternatively, a weakly intrusive auditory display tells the player by sounds of different loudness if he or she is walking in the right or wrong direction when looking for the way to the next checkpoint. We conducted a first usability evaluation with five teams of two players each. The process of the game, the interaction of the players with each other, and additional persons were observed and recorded; the players also answered a short questionnaire. The results are very promising: playing the game was fun, the players quickly got used to the game idea, and the multimodal user interface of the mobile device had been easily understood. The auditory support was considered helpful and a good complement for graphical visualisation.