This paper explores how participatory speculative design enables diverse stakeholders to collectively imagine alternative urban futures addressing complex challenges. Through workshops in Tampere and Helsinki, Finland, we identify recurring themes in the speculative visions developed by participants: transformed governance systems beyond human-centered models, complex body-technology relationships, innovative environmental adaptation strategies, and persistent social stratification despite technological change. The analysis reveals significant insights for urban planning, design, and Human-Computer Interaction (HCI), particularly regarding the design of technologies that mediate governance, embodiment, and environmental relationships. By utilizing a “fictional city sheet” derived from a typology of fantastical cities, participants developed nuanced visions addressing technological governance, climate adaptation, and social transformation. The research contributes methodological insights about structured frameworks for urban imagination and substantive understanding of contemporary concerns regarding urban futures. We argue that participatory speculation represents a valuable complement to conventional urban planning and HCI approaches, particularly for addressing complex challenges that exceed the scope of traditional problem-solving methods and for engaging diverse stakeholders in critically examining technological futures.