In the face of contemporary economic, environmental, and social changes, one of the main challenges facing cities is to build and realise a vision for a sustainable future. To do so, a number of local sustainability strategies are promoted in urban policymaking with the goal of improving citizens' participation and quality of life. The aim is to empower citizens and enable them to be more active in local and global sustainability issues. This paper focuses on identifying and discussing the alternative spaces in which the future of the city can be collectively envisioned, considering processes of socio-ecological change and power relations, consistent with an urban political ecology. The purpose of such spaces should be to link daily behaviour patterns of sustainability with urban environmental governance through processes of participation. In particular we suggest the adoption of an integrative approach between top-down and bottom-up approaches. One example is an experimental process, called the Altrevie project, which took place in a pilot area of the city of Brescia and involved 150 families. The approach is an example of participatory action research. Its first phase was a sample survey to obtain an initial representation of the lifestyles of the residents. In the second phase, residents learnt to measure their ecological footprint and participated in workshops and laboratories to improve the sustainability of their lifestyles. During the project, we identified and tried to promote alternative spaces in which to imagine and build the sustainable city: spaces of alternative consumption which go beyond the traditional market system (according to alternative economic geographies); and spaces of participation that can promote an integrative method between top-down and bottom-up approaches. These different approaches to urban development create unique conditions for seeking sustainability through innovative and participative visions.