Virtual reality (VR) technology has the potential to revolutionize public engagement in the design of urban projects, leading to more sustainable and inclusive environments. This research scrutinizes this potential through a study of elevated urban spaces, specifically the Sky Garden and Crossrail Place in London. Comparing real and virtual interactions, the aim is to highlight their differences and similarities while underscoring the importance of design decision-making for sustainable public places. Through walk-along interviews with 33 visitors in each space and a VR experiment with a separate group of 33 participants, the study analyses the effectiveness of VR as a co-design tool. The outcomes demonstrate that VR positively influences user involvement and allows for the production and real-time testing of design alternatives. Significantly, the majority of participants, who had not physically visited the spaces, could identify design concerns and propose potential activities and features through the VR experiment. These findings were consistent with those expressed by actual users of the spaces. By comparing human activities, circulation, and design concerns in both physical and virtual environments, the research underscores the potential and limitations of VR as a co-design tool for creating sustainable public spaces.