SPOILER
*
*
*
*
*
*
*
*
*
*
*
*
Go back to where you entered this level of the maze, to the room where the ancient book is. In the top left there's a secret door. Go through it. Here you'll find a bunch of kobolds, worshipping a crystal. After you've killed them, search their bodies: one of them has woden stakes on him. Oh, and don't forget to take the piece of the crystal - you'll need it afterwards.