The rise of urbanization, overpopulation, and resource depletion in recent years has triggered interest in developing more efficient solutions that could offer sustainable development and improve the quality of life in cities. The increasingly wider and more advanced availability of computational power throughout the anthropic space—which saw the emergence of the so-called “ubiquitous computing” paradigm—has opened new possibilities for the design of smart cities. In particular, the emergence of Extended Reality technologies (XR), such as Virtual Reality and Augmented Reality, has provided a new interface to bridge the gap between the physical and digital realms, enabling immersive experiences and interactions within Smart City environments. This paper, based on three case studies at different scales of smart environments, explores the current and prospected relevance of XR to both design and experience spaces enriched and characterized by layers of digital information and sensorial interactions.