Urban media interfaces can assume many forms, offering rich possibilities for interactions and social encounters. We focus on a particular type of urban interfaces, namely urban media installations, which are situated, fixed (i.e. non-mobile) and outdoor interactive interfaces enhanced by digital technologies. Drawing on research on play in the context of the smart city, we aim to clarify how the digital and the physical worlds of urban media installations can coalesce into enjoyable and socially thriving playscapes. Two case studies of urban media installations featuring high levels of interactivity and playfulness are presented: the Appearing Rooms, a seasonal art installation in London, and the Mirror Pool, a permanent, large-scale urban installation in Bradford, UK. Each of these interfaces incorporates a design paradigm that differs from the other in terms of context, duration of implementation, and scale. Following a longitudinal approach based on non-participant observations and timelapse photography, we analyse emergent interactions and focus in particular on playful encounters at different levels and scales: from the micro scale of the bodily engagement to the macro scale of the spatial and social configurations. Our case studies highlight that the urban spatial layout is a key element in defining the emerging interactions and encounters around the urban situated interfaces. We suggest, within the premise of the "smart city", that digital technologies can have an active role, with a great potential to encourage playful experiences and shared encounters in urban spaces; yet the digital should be coupled with a careful consideration of the spatial, physical, material and bodily aspects of interactions, that are fundamental to our lived experience of the city.