There's a Pierogi atlas, many maps in different hands, all carefully scribed.
There's a book of dream symbology, from an inworld press. Things like "dreaming about teeth symbolizes financial difficulty. Dreaming about bananas symbolizes a period of hard work." It seems to have been read only through the first two chapters, judging from the binding.
There's a reference book about Pierogi flora and fauna, with an appendix at the back mentioning some of the non-existent and fictitious ones.