The aim of this paper is to consider from a utopian point of view the activities and theoretical positions of Rotor, a collective of architects and designers founded in 2005 in Brussels, which, for the moment, has never explicitly written about utopia. First, we underline how this group is deeply engaged with a question that in the last decades has become more and more crucial for utopian theories and projects: the question of sustainability. We will analyse one of its most recent exhibitions devoted to this topic, “Behind the Green Door”, as well a series of examples that show how their work can change our relationship primarily with construction materials, but not only with them. Then, we consider the relationship between this approach and the work of Charles Fourier. We suggest that despite their apparent distance, their proximity becomes manifest when, instead of the stereotypical notion of phalanstère, we look closer into Fourier's texts and into the crucial role he gives to details. In this perspective, we show how Rotor is valuable to rethink the relationship between architecture and utopia, in coherence with the most recent critical reflections on both of them.