In a new environment, people identify, remember, and recognize where they can comfortably travel. This paper argues that a robot navigator too should learn and rely upon a mental model of unobstructed space. Extensive simulation of a controller for an industrial-strength robot demonstrates how metacognition applied to a model of unobstructed space resolves some engineering challenges and provides resilience in the face of others. The robot plans and learns quickly, considers alternative actions, takes novel shortcuts, and interrupts its own plans.