This paper examines the praxeology of informal educational practices (i.e. how participants produce setting-specific practices to make a tour happen) in the Geophysical and Astronomical Observatory of the University of Coimbra through close analysis of a video-recorded excerpt of a guided tour. Guided visits in informal science settings are important educational events that take place every day in many institutions. Even so, research addressing these activities in detail remains scarce. It is assumed that tours are "structured" interactions, having a stable format in which participants follow predetermined actions. Nonetheless, the results of this study show that the guided tour observed here is highly interactive, with educational practices being co-accomplished by participants (guides and students) with different levels of astronomical expertise. The present study aims to contribute to our understanding of guided tours, and in so doing shows the importance of methods for data analysis sensitive to naturally occurring events.