Build a hidden drawer into your bookshelf that hides as a row of books.
Allows using some of the space in a bookshelf for (secret?) things, while still looking good.

Materials needed:

Sacrificial books (I used an outdated encyclopedia that was thrown away)
Plywood for the drawer (and tools to work with it, if you want to cut it yourself)
Wood glue
Nails
Woodworking clamps
Hot glue gun
Hobby knife
Black marker

Step 1: Prepare the Drawer Plywood

The dimensions of the plywood panels that will form the drawer box will depend on the following things:

The width of all the combined books that will become the front of the drawer
The depth of your bookshelf
The height of your books

I used 12 books, each being 3.5cm thick, bringing the width of the drawer to 42 cm overall. As such the drawer is exactly as long as the combined width of the book backs.

My books were 19.5 cm tall. In order to prevent seeing the drawer on top, the height was set to 18cm.

My bookshelf was about 23 cm deep. However, the books don't stand at the edge of the shelves, so the drawer was designed to be 20cm deep. Keep in mind that the false front of books will add a bit of depth at the end.

You will need three large panels to form the front, back and bottom sections of the box, as well as two smaller pieces that will form the sides. I connected the front and back panels to the sides of the the bottom, so that the side pieces sat on top of the bottom piece (see the sketches). Keep the thickness of the plywood itself in mind. I used 1cm thick plywood, which was probably a little overkill for my box dimensions.

Step 2: Assemble the Drawer

Assemble the five plywood panels into a box using wood glue. Make sure to create right angles.
This works well with a woodworking square. I didn't have access to one and used a large piece of wood instead.

Use plenty of glue and clamp down the panels.

After the glue has dried a little, I added some small nails for additional support. Depending on what should go into the boy, this might not be necessary.

Test fit the finished drawer in the bookshelf.

Step 3: Prepare the Front

Completely remove the covers of the books you have collected, removing all the pages.

Cut off the sides of a few covers of those books that will form the center. Use the material to cut strips the width of your original book using a hobby knife. Hot glue these into the spines of your book covers, to give them some stability and force them back to a roughly book shaped, bowed shape.

The book covers that will be on the very right and the very left, will each keep one side of the cover, that will attach to the side of the drawer, so do not remove the left side of the leftmost and the right side of the rightmost book.

Test fit your collection of trimmed book fronts on the drawer front. There should not be any large, obvious gaps.

Step 4: Assemble & Finish

Using a black marker, mark the edges of the book front elements on the drawer front. Color the surrounding of the markings black, so that possible small gaps between book covers won't be immediately visible.

Attach the book cover elements to the drawer front one by one using a hot glue gun. Start from one side, working towards the other. Try to keep as little space as possible between book covers to give the impression of a neatly stacked bookshelf.

Lastly attach the sides of the book covers at the edges to the edges of the drawer.

Place the drawer into your bookshelf. I thought it looked especially realistic in a bookshelf surrounded by real books.

Done! Enjoy your hidden bookshelf drawer!