A bestiary is a book from the medieval era with pictures and stories of animals. Bestiaries includes real animals as well as mythical animals such as unicorns.
A medieval source of information about animals is a bestiary — a book with descriptions of animals real and imaginary, often with moralizing tales of their exploits. In this respect, bestiaries had a lot in common with fairy tales, which also often end with a moral. Bestiaries often had gorgeous artwork portraying the real and fanciful creatures. If you like reading about centaurs as much as bears, you'd probably enjoy reading a bestiary, which is related to the word beast.