— The creation of a robot capable of navigating in unknown urban environments without the use of GPS data or prior map knowledge is envisioned in the Autonomous City Explorer (ACE) project. The robot has to retrieve direction information solely by interacting with humans. This work presents a human-robot communication system that enables the robot to ask for directions and store the retrieved route information as internal knowledge. The system incorporates theories from linguistics in a mixed-modalities communication interface. It stores acquired information into a topological route graph which is used to give feedback to the human and to navigate in unknown environments.