Kreyon City is a unique experience whose challenge is that of collectively conceive sustainable solutions for the city. No-one is able to conceive the whole city alone. On the contrary the contribution of each and every one are highly important. Participants are challenged in bootstrapping a whole city made of houses, industries, schools, services and infrastructures, without an underlying blueprint. Everyone has the opportunity to shape his/her own ideas, by creating new parts of the city of restructuring and improving elements built by others. The emerging city is monitored through cameras that, like observation satellites, allow to visualise in real-time important features of the city, like the number of inhabitants, the energy consumption, the levels of pollution, etc.