“A Cidade de Portas” is a documentary about the city as the frontier of the thought of Nuno Portas, visionary architect, urban planner and professor emeritus at the University of Porto - Portugal. His reflections, his architectural and urban projects, as well as the urban plans he coordinated and the books he wrote, raise a deep debate about the city as a cultural object, full of multiple ambiences and spatial contradictions, which reflect and define everyday experience make “being urban”.