Interactive artistic installations represent avant-garde forms of Contemporary Art. They are artistic works able to change their behavior in response to the behavior of the viewers, turning them into (more or less) active participants. This paper discusses an interactive installation the authors developed during the beginning of 2012 for the St. Elmo Castle in Naples, Italy. In this installation the audience determines the evolution of the life cycle of specific plants, in terms of an opening/closing process. The paper proposes some reflections on this case study, especially about the engagement dimension promoted by the work.