In The Sinking City 2, there is a unique Ritual Book located in the annex. Obtaining this book is quite challenging. First, you need to head to the library. There, you can operate the roulette mechanism. Turning it will move the bookshelves, and once they are shifted, you'll be able to see a special door.
How to Obtain the Ritual Book in The Sinking City 2 Annex