| “ | Welcome to my reading room. (...) Dean, every notebook on this particular shelf tells a version of how you die - you specifically. | ” |
Death's Reading Room, also referred to as Death's Library, is a special library that contains notebooks, each detailing a version of how a person may die. Only Death can read the books of someone's death.
History
Season 13
In Advanced Thanatology, after Dean dies temporarily in order to find the location of the bodies of the Meadows' House ghosts, Billie reveals herself as the new Death to him and transports him to her reading room. Billie explains the significance of the room and the books to Dean before eventually resurrecting him.
In Funeralia, the Reaper Jessica reveals that all of Rowena's books depicting her ultimate fates end the same way with Sam killing her.
Season 14
In Nihilism, after Dean traps Michael in his mind, all but one of the notebooks depicting his potential fates change to Michael escaping and using Dean's body to destroy the world. Billie gives this book to Dean so that he can make a decision on what to do with the information.
In Prophet and Loss, Dean reveals that the book Billie gave him reveals that the only solution is for him to trap himself and Michael in a Ma'lak Box and it gave him directions on how to create one.
Season 15
In Galaxy Brain, Billie reveals that even God has a book in the library which reveals how God dies. The books are not written by God or even Death but rather they write themselves based on choices and circumstances. God had no choice but to write himself into the framework of the world which makes him vulnerable. No one can read their book unless Billie lets them, not even God. All Billie will reveal is that God's book contains Jack and the Winchesters.
In Unity, Sam is able to access the room using the Key to Death where he finds the Shadow searching for Billie. Though the Shadow has found God's book, only Billie can read it and Sam convinces the being to give the book to him.
In Despair, Billie retreats to her reading room after being mortally wounded by Dean with Death's Scythe. Billie has the room warded by a Reaper for protection against the Shadow.
Dean and Castiel later enter to kill Billie after believing her to be targeting their friends saved from Apocalypse World. After revealing that Chuck is responsible for the recent deaths, Billie chases the two to get revenge upon them before she dies.
Layout and contents
The reading room contains many shelves of books detailing the death of an individual. Curiously there is an entire shelf dedicated to a potential death that Dean may experience. Billie told Dean that some of these books say that he may potentially die from a heart attack, being burned by a red haired witch, stabbed by a ghoul in a graveyard, and "on and on". After Dean traps Michael in his mind, all but one of these notebooks change to Michael escaping and using Dean's body to destroy the world. These books can be taken to the physical plane as seen by Billie's ability to give Dean the book containing the one different fate in the Men of Letters bunker.
Billie later reveals that the books write themselves and that not even God can read them without her permission or that of an incarnation of Death. At the very least Chuck's Death Book can't even be opened by anyone but Death and once it is opened, the book appears to be blank to anyone else.