Here is a puzzle I threw at my D&D group a few years back. So, I figured I'd share.
The group has come to a large library. Amongst all the shelves are very organized books. There appears to be a numbering system on each of them. None of the books move when touched. They are also dust free.
On the far wall is a shelf that appears to be missing some books. When approached there is a thin layer of dust on the shelf depicting the outline of thirteen missing books.
While looking around the room, the players find scattered around the floor the missing 13.
One of the adventurers goes over and picks up a book. He looks and sees a title, author, and some interesting numbers on the bottom.
The title and numbers read:
I am not the butt I am the what? - Heinrich Heine [813.520]
After a moment the other adventurers go around and pick up all the other books. When they do a message appears on the wall:
Find the song to move along.
Below the message a strange grid shows up:
[0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0] [0.0]
They look at the titles and authors for each of the remaining books in no particular order:
You, You're, Your - Gerund das Hauptwort [811.655]
Meree Garba - Unknown [808.204]
Canada Book 1 - Moins Ada [808.101]
The beginnings of a condition - John Backus [808.288]
Just a little Book 1 - Walter Scott [808.033]
Becweþan - The Descendants of Thes Auri [811.054]
Just a little Book 3 - Walter Scott [809.111]
To pull something towards you - Juan Pablo de Bonet [808.355]
Just a little Book 2 - Walter Scott [808.289]
To Open the Doors of Durin - J.R.R. Tolkien [811.888]
Canada Book 2 - Moins Ada [810.001]
Two, Too, To, Tu Tu, - Arthur Moeller van den Bruck [809.034]
The players also noticed that on every book where it has Book 1, 2, or 3, that part of the title is faded, and hardly readable.
After all the titles are read the outline of a door appears below the grid and the space for two words appear.
They gather around and attempt to solve the riddle to open the door.
Note: this is my first puzzle to post, so feel free to edit the tags as necessary.