Hardcover is your best bet and old encyclopedias, reference manuals and your old college textbooks can come in handy here. You'll also need a pen, an exacto knife and glue for this.


If you can't find a large book at home, try the thrift store or a used book store. Or, ask for one via a site like Freecycle.
If you are hiding a diary inside it, measure the ability of the book to cope with this object before cutting it.
 Flip over the first 20-40 pages or so, depending how much room you want inside the book.
 Make it the size you want, leaving an inch (2.5cm) allowance as borders around the hole space, or it will look too obvious when completed.
 Repeat the last two steps if your book is particularly thick.
 The pages of the book will then stick together and form strong walls for the hideaway compartment. Also apply glue to the backside (either the back cover or one of the remaining pages of the back). This will make a box, and your things won't fall out quite so easily.
 These will press the glued pages together. Set aside and let it dry.
 You now have a secret compartment where you can hide your special stuff. Snap the book shut and put it away in the bookshelf for safekeeping.
Find a thick and very large book that you won't ever want to read again.
Open the book.
Draw a rectangular shape on the next page from the ones flipped over.
Carefully cut out the rectangular hole with the Exacto knife.
With the hole now in the book, use an old painting brush to start coating the inside edges of the hole with glue.
Weight the book down with a few heavy books.
Fill with your goodies.
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