The GUIDE system has been developed to provide city visitors with a hand-held context-aware tourist guide. The system has been successfully deployed in a major tourist destination and is currently at the stage where it is publicly available to visitors who wish to explore the city. Reaching this stage has been the culmination of a number of distinct research efforts. In more detail, the development of GUIDE has involved: capturing a real set of application requirements, investigating the properties of a cell-based wireless communications technology in a built-up environment and deploying a network based on this technology around the city, designing and populating an information model to represent attractions and key buildings within the city, prototyping the development of a distributed application running across portable GUIDE units and stationary cell-servers and, finally, evaluating the entire system during an extensive field-trial study. This paper reports on our results in each of these areas. We believe that through our work on the GUIDE project we have produced a blueprint for the development of interactive context- aware systems that should be of real value to those in the community who wish to develop such systems in a practical environment.