Music plays a vital role in accompanying all manner of our experiences. Soundtracks within films, video games and ceremonies possess a unique ability to enhance a narrative, suggest emotional content and mark key transitions. Moreover, soundtracks often achieve all of this without being the primary focus, on the contrary they typically assume a supporting role. The proliferation of mobile devices increasingly leads us to listen to music while on the move and musicians are seizing on locative technologies as a tool for creating new kinds of music that directly respond to people’s movements through space. In light of these trends, we consider the interesting question of how composers might set about creating musical soundtracks to accompany mobile experiences. What we have in mind are experiences such as guided walks, tours and even pervasive games. The novelty of our research here is in the music serving as an accompaniment to enhance a location specific activity, much as a soundtrack does for a film. This calls for composers to take into account the key features of the experience, and its setting, to gently complement them through the music. We examine this process from a composer’s perspective by presenting ‘from the field’ an account of how they address the multifaceted challenges of designing a soundtrack for public sculpture park. We chart a composer’s rationale as they developed a soundtrack for this site over multiple iterations of design, testing and refinement. We expose key relationships between the raw materials of music (melody, harmony, timbre, rhythm and dynamics) and those of the physical setting, that enable the composer to gracefully mesh the music into the fabric of the space. The result is to propose a set of recommendations to inform the composition of mobile soundtracks that we intend to guide future practice and research.