Analysing the evolution of a site and the behaviour of its users has become a crucial work in order to let the webmasters and the owners of web sites to enhance their site in terms of structure and contents. Data mining techniques provide many metrics and statistics useful to understand the structure of a website, and the use its users make of it, but they are still not easy to interpret and to understand. Most of these metrics can also be combined, in order to discover new trends and patterns. We present a preliminary prototype of an exploratory search system for web mining which main goal is to provide a set of tools and visual representations that allow the user to explore and to decide how to represent the available data. This approach defines a system that will help us to evaluate the usability of the implemented interactions and visual metaphors.