You are probably already familiar with the classic “Secret Book Compartment” project. On Make’s YouTube Channel alone, you can find 4 different variations of this project. The basic concept is simple. You hollow out a large book and you use the cutout space to hide stuff. Unfortunately, most versions of this project have one major problem. You can only hide objects that are smaller than your book. However it is possible to hide larger objects by combining multiple books into one large multi-book container.