Although artistic augmented reality (AR) and mixed reality (MR) experiences have been discussed in multiple scholarly fields, when it comes to interaction design, comprehensive accounts of actual design practices are rare. To expand our knowledge of design practices, this PhD dissertation brings together choreography and interaction design, approaching MR as site-specific performance. More specifically, choreography as an expanded practice is used to encourage discussions about the creation of MR experiences in public spaces. The research project involved practice-based research and the creation of three public site-specific MR walks in Göteborg and Mölndal, realised in collaboration with an artistic team and stakeholders from the art, cultural heritage and information technology sectors. The dissertation shows that a choreographic approach provides concrete ways for crafting relations between time, space, bodies and imagination in AR/MR experiences, demonstrating that technology is imbued with site-specific power relations, ethics and aesthetics. These contributions are both practice-oriented and theoretical. They include an expansion of our knowledge of embodied interaction and its relevance to public space, an articulation of choreography as a broad practice that can be applied to technological design and a distinct set of composition practices for site-specific AR/MR experiences. Together, these contributions result in strategies and critical reflection on how AR/MR experiences may be used to reactivate public spaces and their political significance in society through critical, embodied and artistic techniques.