Bookcase door! I've got a small, maybe 8'x10' room that I'm going to make into my library. I'm going to attempt to do this to the door, depending on clearance, etc. Opposite wall will have a window seat with side walls having nothing but bookshelves.
Reminds me of why Belle was my favorite Disney princess. Because she had that awesome library with a rolling ladder! You need a ladder for this one. And I love that all the cubbies are different sizes.