Every now and then you run across a website that is complex. It's conventional navigation system is of no use in finding what you want because there are so many links hidden in so many tabs. What I do next is head for the site map. There I can get an overview of the site and conceptualize the logic that went into its structure, and more often than not, I find the link to what I'm looking for.
I'm not completely alone in my reliance on site maps, but nearly. According to a recent study by the Nielson-Norman Group, only about seven percent of web users rely on site maps.
Site maps have another very vital function: they can serve as a blueprint from which to construct the site in the first place. For visitors it answers the question, "what do I want to find in this site?" For the site owner, it answers the question, "what do I want to display in this site?"
When the site map fails, I generally ask Google to search the site for me. I find it does a better job than just about anything.