The present thesis project discusses the matter of definition of the public space, in a conceptual and morphological content, from the users of that space themselves, through the organisation and application of a method of participatory design. Chalandri square is selected as case of public space. We focus on the phenomenon of open musical improvisations (Jam) that happen there, with the initiative of the local habitants. We pursue to involve with them in an exchange of ideas and thoughts of the space, of how we would like the square to be as the place where the jams occur. Our meetings with them happen in real time, evolve in the public space and are accompanied by objects that function as “tools” to support our method. With these objects is triggered and recorded the production of the ideas above. Our method unrolls in an experimental manner, step by step, is being redefined each time by the participation of others in it and is divided in three basic levels. The first level concerns the installation of the objects in the space of the square, by ourselves, during two jammings, with the purpose of the introduction of an architectural process that concurs with the musical improvisations and in which participate the people that are located in the space at that time. Through these open processes which evolve at the same time, the public character of the square is enhanced and an investigation of the desires linked with its space occurs. The second level takes place in the square and in a park close to it, where we set up the field for conversations about the square, the jammings in it and the desires mentioned above, to happen. This procedure is in the form of a workshop and is realised with the participation of people that had attended the square’s jammings. The third level is the in-situ application of the above suggestions as the preparation of the square for another jam. During this last jam, the interventions were used by the people that took place in their conception and design process as well as from the rest of attendants.