What is the Midnight Library in the novel, The Midnight Library?

The Midnight Library is a figment of Nora's imagination. In the midnight library, Nora is given the opportunity to try out a multitude of lives, but she always ends up right back where she started-- in the library, feeling dissatisfied. The library comes to represent Nora’s melancholy and constant thirst for something which does not exist without a desire to live: happiness.