The Library of the Neitherlands is intended to be the source of all knowledge and all books in the world. There are books about magic and books with the entire knowledge about a person: what has been and what will be.
The Poison Room Edit
A room introduced in season 2 episode 10. It is a room with dangerous knowledge, not accessible for the public. A book about how to kill a god is in there, which is the book Kady needs.
TV Differences Edit
There are major differences between the book and TV series. In the TV show you get introduced very fast to the library and it is easily accessible - and open for the public. In the book series, the library is closed and not open for the public.