It's a legal deposit library, same as e.g. Library of Congress. Which means almost every published book, magazine, and newspaper and many other works published in Norway, as well as large collections of Norwegian works published abroad (such as thousands of Norwegian-language newspapers published by the Norwegian immigrant communities in the US) for many decades and a large proportion of the same from the last 200+ years are stored there.

They do also crawl websites (or at least did) in the .no tld.