Single-click 3D navigation allows users to navigate a virtual space with a single click of the mouse or tap of the finger. As such, it is appealing for its simplicity, a trait especially important for mass consumer applications. In addition, single-click navigation is also suitable for incomplete or sparse models, and is thus commonly used for navigating partial 3D reconstructions based on panoramas or structure from motion. In this paper, we give a description of the design space for single-click 3D navigation, showing that the crucial design choices typically include a viewpoint selection algorithm and a viewpoint visualization. We further present a brief user study on viewpoint visualizations for single-click navigation. Our results indicate that current systems lack adequate visualizations for navigating complex environments and that the viewpoint selection algorithm is perhaps most important, requiring more investigation.