Urban-development controversies usually involve complicated struggles over knowledge. One way to analyse them is the framework of epistemic injustice - the feeling of one's knowledge not being acted upon - often experienced by vulnerable groups. The present case shows that middle-class citizens are also affected as the controversy pits different understandings of 'green' against each other. Even activists in well-resourced positions protesting the development of a beautiful island, sense the weakness of official, modern types of evidence. They are, however, willing to host activist-artistic experiments that highlight various historical legacies of modern life, simultaneously challenging conventional ways of knowing and definitions of what is environmental. The paper interprets this form of activism as making the island itself appear as a crystallisation of harmful processes, diffused in time and space and involving diverse types of actors. Difficult to capture with modern ways of knowing, these processes are nevertheless embedded in the natural and cultural heritage accumulated over time in urban landscapes.