The walkthrough is once again really vague.
I vaguely remember you have to buy it with coins that you can find in-game, maybe they are hidden. It's been almost a year since I played.
On the top right of the town there should be a big building, you can spend those coins somewhere in that building. After you buy it, you should be able to access it by going to the book that's in front of the entrance [I guess there's more than one book, try them all]