As virtual environments grow in complexity, size, and scope users will be increasingly challenged in assessing the situation in them. This will occur because of the difficulty in determining where to focus attention and in assimilating and assessing the information as it floods in. One technique for providing this type of assistance is to provide the user with a first-person, immersive, synthetic environment observation post, an observatory, that permits unobtrusive observation of the environment without interfering with the activity in the environment. However, for large, complex synthetic environments this type of support is not sufficient because the mere portrayal of raw, unanalyzed data about the objects in the virtual space can overwhelm the user with information. To address this problem, which exists in both real and virtual environments, we are investigating the forms of situation awareness assistance needed by users of large-scale virtual environments and the ways in which a virtual environment can be used to improve situation awareness of real-world environments. A technique that we have developed is to allow a user to place analysis modules throughout the virtual environment. Each module provides summary information concerning the importance of the activity in its portion of the virtual environment to the user. Our prototype system, called the Sentinel, is embedded within a virtual environment observatory and provides situation awareness assistance for users within a large virtual environment.