This article contributes to an exploration of the relations between culture and policies for sustainable development in cities. It discusses the potentials to advance a cultural approach to sustainable urban development by enabling urban "spaces of possibility", relating them to institutional (social, cultural, and political) innovations. Based on empirical research in the two cities of Hamburg and Hanover, the article examines the relations between four selected cases of cultural actors/initiatives and the differing policies of the two cities, pointing at the seized or missed opportunities for innovative forms of transversal partnerships through a culturally sensitive urban policy.