The World Wide Web is a distributed, heterogeneous and semi-structured information space. With the growth of available data, retrieving interesting information is becoming quite difficult and classical search engines give often very poor results. The Web is changing very quickly, and search engines mainly use old and well-known IR techniques. One of the main problems is the lack of explicit HTML page structure, and more generally the lack of explicit Web sites structure. We show in this paper that it is possible to extract such a structure, which can be explicit or implicit: hypertext links between pages, the implicit relations between pages, the HTML tags describing structure, etc. We present some preliminary results of a Web sample analysis extracting several levels of structure (a hierarchical tree structure, a graph-like structure).