During summer heatwaves, public spaces are frequently warmer than human thermal comfort preferences in a majority of Australian Cities. Citizens’ preferences of public space elements and supportive features during heat-stress conditions are under particular focus in this paper. Outdoor activity choices in different thermal environments were surveyed in Adelaide from September 2013 to April 2014. This post-activity survey indicates that necessary, optional and social activities decreased during outdoor heat-stress more than any other thermal conditions. Outdoor activities were chosen the most in neutral and warm thermal environments. Outdoor activity choices were affected significantly by the magnitude of solar radiation. Tree canopy, shading (from buildings or temporary elements) and water features were the most attractive public space features for outdoor participants during heat-stress conditions in Adelaide. Meanwhile, essential shopping and dining facilities and social events affect citizens’ outdoor activity choices during heat-stress conditions. Thus, increased green infrastructures and supportive land uses are a prerequisite of urban transformation for climate change adaptation.