Navigation & URL structure
The navigation structure is the way a site visitor finds his or her way around the site. As previously mentioned, simple text links are best here - which is why many sites have a text-based sitemap as well as their java or graphic based navigation links.
The wording of the links is a key factor, too - see the Internal Links section.
Related to the navigation structure is the URL structure of where the files are placed.
It is much better to have a URL structure in the following format:
www.vam.ac.uk/fashion/index.html
than a series of dynamically-generated query strings, or to house the pages in an extraneous folder, such as:
www.vam.ac.uk/collections/fashion/index.html
where "/collections/" is the extraneous folder.
If there needs to be such a folder, however, it is better to have named it something appropriate - as has been done in this case - based on keyword research, such as "/collections/" or "/exhibitions/" and the like, rather than something meaningless, such as "/123/".
Tying these together, it is best practice to have the navigation structure directly related to the URL structure, such that the sitemap links point to the relevant folders within the site - i.e. those that are related through having common words and phrases.