1) Get a really thick book. We used "My American Journey" by Colin Powell. This is not a book we would typically have on display at our house, nor one that either of us would probably read, but it was definitely thick enough! I think the key is to have a book that no one would really suspect of being anything but a book. And, you don't want one that's too interesting because then everyone will pick it up. That would defeat the purpose of hiding anything inside the book! When you see these things in the movies people tend to use the Bible, but I couldn't bring myself to rip pages out of a Bible. Colin Powell will have to do! (FYI - we left the beginning pages alone so you can still flip through the pictures like a real book!)
3) Open up the book to the first glued page (remember to keep that one unglued page where you really want the safe to start unglued, unmarked and uncut for now). Using a ruler, measure and mark 1/2 inch from the edges and the spine of the book. This is the line you'll be cutting on. You can really make this any shape, but we cut 1/2 inch in from the edges. Buy a very sharp pen knife or x-acto knife and start cutting on those lines you just marked. I found it easiest to pull the knife toward my body and to spend some extra time on the corners for things to come out nicely. The straighter and more careful you cut, the nicer the inside of the book will look.
4) Be careful while you're pulling out the pages. If you try to do too many at once, you could pull more than you want and end up messing up the edge of the book. This almost happened to me, but I saw it before it was too late. I think I tried to pull out a page that wasn't cut all the way through and so it wanted to rip the entire page out, not just the section I had cut out. We left about the last half-inch of the book intact, but you can cut in as deep or as shallow as you want.
5) Using the same technique you did for the outside of the book, glue the inside edges of the pages inside the hole to reinforce everything. During this step you'll also put a thin layer of glue on the top edge (the original page that you marked with your cutting lines) and then glue down that one page you've kept out this whole time. Again, close the book, weigh it down with something heavy, and wait 30 minutes before going on to the next step.
7) The edges on the inside of our safe were a little rough from jagged cutting, so we decided we were going to line the inside with felt. To do this, I brushed on a layer of glue on the bottom of the hollowed-out area. Then I pressed down my sheet of felt. Rather than cutting separate strips for the sides of the safe, I used my pen knife to cut through the corner area so I could make a straight edge. Then I glued around the edges, pushed down the felt and it was all connected. I used a regular pair of scissors to snip off the excess to make it flush with the top of the page. Voila! You're done!