The sense of dwelling in a place is founded on multiple sources. Seeing and recounting the resultant constructions remain one of the major challenges we face in attempting to understand usages and the capacity of a place to renew itself while maintaining what makes it specific and whose ambiance is both a catalyst and a revelatory agent. Based on Etienne Souriau’s works on modes of existence, reviewed by David Lapoujade, we will study the ways in which it is possible to see in a projectual framework a retro-prospective approaches of dwelling-in-ambiances. To illustrate these propositions, we will rely on an urban project that we developed: “L’Affaire de l’aqueduc de la Reine Pédauque” (Toulouse, France).