When we think of service robots for public spaces, we often consider human-like systems that socially interact with users in short-term and dynamically changing scenarios. Many design assumptions exist for this type of robot, but what about for a service robot that needs to interact with people in a very task/role-oriented manner? This paper presents a research-through-design approach, which explores the idea of a "luggage-carrying robot guide" for train stations which supports travellers. Contrary to the classical paper describing the requirements, design, implementation, and evaluation of the robot, this work presents an exploratory design study. An interdisciplinary team composed of two industrial designers, a roboticist, and a social scientist performed a study with users to establish a design space for the aforementioned service robot.