Brazilian cities are structured around a socio-spatial segregation that shows a strong prevalence of private spaces over public spaces. This situation creates a constant replacement of the meanings assigned to public spaces, which are turned into consumption spaces, stigmatized as risky and abandoned by the government. This paper approaches “emerging practices in design” aimed at designing sustainable cities in developing countries through the production of “utopian spaces”. These practices can be understood as living laboratories to generate social innovation. In this article it is presented the design projects developed by three Brazilian groups: “Muda”, in São Paulo; “Praias do Capibaribe”, in Recife; and “Opavivará”, in Rio de Janeiro. The data was collected during a field study though ethnographic participant observation and qualitative interviews with the project creators and citizens involved. Three aspects were analysed: participation, materialization and subjectivity. The aim of this study is to understand how these design practices can explore the feelings fostered by public urban spaces, as well, how they interfere more effectively in the city’s culture of participation. In this analysis, design is understood as a performative action that prioritizes both the social and the cultural dimensions of spaces and objects. In the closing remarks this study shows that these experiences have a character of micro practices empowering the actions of each individual involved in the collective body, finds effectiveness to arise the sense of community in the city. The grass-root nature of this approach could be seen as an obstacle for its use on a wider scale, but the efficiency of these actions in promoting deep social changes should encourage public and private urban institutions to implement policies that enhance their development.