A virtual world is a computer-based simulated environment intended for users to inhabit and interact via avatars. These avatars are usually depicted as textual, two-dimensional, or three-dimensional graphical representations, although other forms are possible (auditory and touch sensations for example). Some, but not all, virtual worlds allow for multiple users. The computer accesses a computer-simulated world and presents perceptual stimuli to the user who, in turn, can manipulate elements of the modelled world and thus experiences telepresence to a certain degree. Such modelled worlds may appear similar to the real world or instead depict fantasy worlds. The model world may simulate rules based on the real world or some hybrid fantasy world. Examples of such rules are gravity, topography, locomotion, real-time actions and communication.