What is the best approach for a sitemap for a very large website?

I'm currently working on a new website for a university. The website is going to have up to 6000 pages with a depth of six or so levels.

Now the clients wants a visual sitemap, a graph representing the structure of the website, which can be used for finding a particular page. The only way I see this happening is using a dynamically created graph, showing maybe the next three levels.

Is there a good example of a sitemap this size anywhere?

(We do have a powerful search as well, and I guess people would use that instead anyways.)