1. In a VRU engine operating on a host computer to model a VRU space, a method for operating a VRU portal, comprising: generating a signal indicating that an avatar moving in the VRU space in response to input from a client device has triggered an entry transaction with a portal object of the VRU space; identifying the avatar; determining whether a custom destination has been defined for the portal object and the identified avatar; if no custom destination has been defined for the portal object and the identified avatar, causing the avatar to enter a default destination environment for the portal object; and if a custom destination has been defined for the portal object and the identified avatar, causing the avatar to enter a custom destination environment that is distinct from the default destination environment.