This paper describes work carried out as part of the GUIDE project at Lancaster University. The overall aim of the project is to develop a context-sensitive tourist guide for visitors to the city of Lancaster. Visitors are equipped with portable GUIDE units which in turn provide interactive services and dynamically tailored web-based information reflecting the visitor's preferences and environmental context. In contrast to existing tourist systems all information in GUIDE is obtained dynamically using a city-wide wireless network infrastructure. The paper presents an overview of the GUIDE system, with particular focus on our design of an appropriate object model, capable of handling the high degree of flexibility required by GUIDE. In addition, the paper includes the results of our requirements analysis, the web-based application that has been developed to meet these requirements and our approach towards communicating information to portable GUIDE units in a timely and scaleable manner.