This research explores the usage of freely available open-source resources for the deployment of a plug-in free web-application interface for 3D geospatial data to visualize energy related modelling and simulation results. Such plug-in free web mapping applications will be essential for future cartographic web applications as forthcoming web browsers will no longer support the usage and installation of those plug-ins used in the past. As a proof of concept, a 3D city model of the city of Karlsruhe in Germany consisting of over 87,000 buildings is used as a case study. This data set was compiled using OpenStreetMap data and outputs from energy simulation models. The CityGML format is used for data storage of this multi-domain data set. In order to ensure independence from browser plug-ins, HTML5 and freely available JavaScript libraries are used for the creation of this application. Multiple analytical cartographic and geospatial functions such as cartographic classification, attribute selection, descriptive statistics, spatial buffer analysis and the retrieval of modelling results from a PostgreSQL and PostGIS data infrastructure are implemented in this interface. This paper further discusses some case studies, future enhancement opportunities of the proposed interface and experiences gathered during the interface development process that would help other cartographers and GIScientists in developing future native 3D web mapping applications.