This paper describes the development of 3D models and applications for the district of Mülheim South, Cologne, Germany, within the framework of the Fraunhofer Society’s project “City of Tomorrow”. GIS technologies are used as support for the implementation of a holistic approach to sustainable urban development as part of the Cologne smart city efforts. 3D GIS visualisation technologies are applied not only for the district in its current state, but also for simulation of future scenarios of sustainable and innovative development. Web-based applications are under development to allow a clear presentation of the new city development projects and scenarios, and to facilitate future citizen participation in the planning and decision making process.