We describe techniques for managing large amounts of data during an interactive walkthrough of an architectural model. These techniques are based on a spatial subdivision, visibility analysis, and a display database containing objects described at multiple levels of detail. In each frame of the walkthrough, we compute a set of objects to render, i.e. those potentially visible from the observer's viewpoint, and a set of objects to swap into memory, i.e. those that might become visible in the near future. We choose an appropriate level of detail at which to store and to render each object, possibly using very simple representations for objects that appear small to the observer, thereby saving space and time. Using these techniques, we cull away large portions of the model that are irrelevant from the observer's viewpoint, and thereby achieve interactive frame rates.