How to make a secret hollow book.
I tried this a half-dozen times when I was a kid, during a couple-year window when I thought I’d be a spy when I grew up. There’s a book somewhere in the kids section of the Rayne public library that’s sort of a kid’s guide to being a spy. I checked it out about 300 times. Couldn’t find it a couple of years ago when I tried hunting it down.
(It was awesome. And even vaguely transgressive, with stuff on how to hide things from your parents, how to use a mail drop on a vacant lot, etc. It sort of explains my weird interest in the products of Paladin Press around sixth grade and a later [purely theoretical] interest in phreaking. That all kind of freaked out my grandma, although not as much as when I requested The Anarchist Cookbook via interlibrary loan around eighth grade. That got me a talking-to.)