We present an interactive installation with life-size virtual agents that inform, entertain, encourage, and assist visitors during the process of building a car. It will be installed as an exhibit in an automobile theme park. Visitors can take car elements from a shelf and put them on a workbench. The virtual agents continually comment the visitor’s actions and the current state of the construction. We use Radio Frequency Identification (RFID) devices to monitor the location of the car elements. This technology allows us to design a natural, unobtrusive and robust interaction by letting the visitors using real objects to communicate with our virtual characters. We show how such an interactive presentation can be created with our SceneMaker authoring tool. We address the problem of authoring content for a large number of combinations and we explain how to design the interaction for an installation where visitors can do anything at anytime.