One of the oldest hypertext usability principles is to visualize the structure of the information space to help users understand where they can go. On today's Web, site maps are a common approach to facilitating navigation. Unfortunately, they are often not very successful at it. We conducted a usability study of site maps on 10 websites, and our main conclusion is that users are reluctant to use site maps and sometimes have problems even finding them. Considering that site maps could be particularly useful to people who are lost, it is not good news that they are often hard to find.