User-generated content (UGC) is already incorporated in several computer game instances wherein the players may create, edit and release their own content to the game world, thus influencing the game's evolution as well as the experience of other players. Lately, pervasive games have emerged as an exciting new development in gaming extending the boundaries of play out in the real word. The effectiveness of pervasive games in creating immersive live-action game experiences principally depends on the correlation of the game content with actual physical elements. To address this issue, most pervasive game prototypes so far have been bound to specific locations, while game content has been manually edited by the developers; they have also been heavily dependent on the mediation of orchestration teams. Nevertheless, the capacity of pervasive games to be staged anywhere (i.e. their portability) is critical for their wider adoption and commercial success. Since the manual creation of game content is not feasible in portable games, UGC remains as the only practical option for content provision. Notably, the impact of UGC has not been studied so far in the pervasive games literature. This article introduces Barbarossa, a pervasive role-playing game based on UGC. Barbarossa serves as a testbed for investigating the effect of UGC under diverse technical, functional and game play characteristics. The user trials of Barbarossa confirmed that the effective use of UGC can enhance the quality of experience perceived by players and indirectly serve as a useful orchestration tool. We also document best practices with respect to the effective use of UGC in pervasive games, which could be useful to future developers.