The present contribution deals with the required scale of performances regarding an adequate simulation environment for recent and future challenges of urban development planning based on the concept “City Experimental Lab, CEL”. This paper issues concrete project experience covering the capital city of Upper Austria, Linz. Such CEL could and should act as an “expert system” in the preliminary stages of decision-finding, making available all particulars regarding decisions to the politicians, the planning administration, outside advisors and particularly to the citizens concerned in the suited present-day manner. It could be used for work sessions of planning- or design councils, expert hearings, for the continuous information of citizens on present planning work at the various degrees of concreteness and commitment, etc.. Thus those possibilities are to be enhanced which turn the present city configuration into a virtual experience by integrating visions, utopias and the future developments.