The Post-car Ile-de-France project (funded by Mobile Lives Forum, SNCF) investigates the hypothesis of an abrupt transition towards lifestyles that depend less on the use of personal vehicles. Its main goal is to explore with people the possible impacts of this scenario on their lifestyles and on the way we should design cities and territories. In such perspective, a serious game prototype has been developed, allowing gamers to interact with a virtual simplified urban environment, in order to explore the possible impacts of a drastic limitation of the use of personal vehicles on urban life. That first step has a very precise purpose: opening up people’s mind by letting them face – in a friendly and intuitive way led by personal experimentation – the multiple constraints they would face as urban actors in such situation. Building this shared common baseline is crucial in the perspective of engaging public participation of citizens, planners and deciders.