1. An interactive mixed reality system, comprising: a physical model of an object being interacted with; a virtual model, stored in a memory, of features of the object being interacted with, the features comprising internal or hidden features of the object, wherein registration is provided between the virtual model and the physical model such that internal or hidden features of the object are underlaid with the physical model; a tracked instrument for interacting with the physical model; and a simulation module accessing the virtual model stored in the memory and providing a corresponding interaction with the virtual model when the tracked instrument is being interacted with the physical model.