Introduction: The Secret Box

At first glance, there is just an ordinary box, with a seemingly empty inside. However, that is not really the case - with a special key, only you are able to open a secret compartment within the box where you can put your prized possessions!


  • A cardboard box, or pieces of cardboard
  • Duct tape
  • A toilet paper roll
  • A wooden stick or skewer
  • Scissors
  • A box cutter or scalpel
  • A marker

Step 1: Gather Pieces of Cardboard.

Any standard rectangular box will work, or if there are scrap pieces of cardboard lying around, you can use those as well. If you have a rectangular box, cut the tape where the box is being held together and unfold it. Then, cut the rectangular portions out where the creases are at to create several cardboard boxes and squares. In total, you need 6 squares to create the sides of the box, or you can leave some as rectangles. In my example, I used two rectangles and 2 squares.

Step 2: Fold the Cardboard Pieces.

This step only applies to those that have used rectangles instead of squares. Fold the rectangles in the middle so that two squares are essentially created.

Step 3: Create the Turning Mechanism.

Using the scalpel, carefully cut out two cardboard circles that are larger than the end of the toilet paper roll, leaving about a 1 cm margin on all sides. Then, cut two slits into each circle by placing the toilet paper roll onto one and drawing a border around it. After tracing the border, use the scalpel to cut approximately 2 cm worth of the border on opposite sides as shown in the image. Once the slits are created, use the scissors to make them bigger, so they are about half a centimeter wide. Then, use the skewer to poke a hole into the center of the circles. *The black tape in the picture is just for decoration.

Step 4: Create the False Bottom.

Next, cut the wooden skewer into two pieces of around 4 cm length. Then, insert these pieces into both ends of a square of cardboard(which is here made of two smaller rectangles taped together) by pushing them into the folds of opposite sides at about 6 cm from one end. Only push them in just enough so that they stay inside.

Step 5: Create the Key.

Now, take the toilet paper roll and use the slits you cut into the cardboard circles earlier to cut out two prongs in the toilet paper roll. This can be done by cutting out rectangles from the top of the roll that are about 3 cm deep. These measurements are just guidelines, but you can make many variations to the key if you want it to be more complex, for instance, by adding more prongs. Next, take any leftover cardboard and cut small rectangles that are about the size of the prongs, and glue them to the inside as shown above. For extra support, you can cut another circle like the ones mentioned in the previous step and push it onto the key.

Step 6: Cut Holes in Two of the Cardboard Squares.

Using the scalpel, cut a circle into the side of one cardboard square, that is slightly smaller than the cardboard circle cut out previously, but is wider than the diameter of the toilet paper roll. This circle should be located at the bottom left corner of the square, about 6 cm from the left side, and 5 cm from the bottom. After doing so, poke a hole into the center of this circle you just made and cut two rectangles from the opposite sides of the circle. Then, place it back into the hole with the rectangular gaps on the top and bottom, and ensure that the key is able to now fit into the side of the box. In the other cardboard square, cut a set of slits where your key can fit into using the key to trace them. Then, poke a hole into the center of the two slits.

Step 7: Assemble the Box.

Using duct tape, tape together four squares of the box, putting the squares modified in the previous steps at opposite ends. Tape another square to the bottom of these, which will be the bottom of the box. Then, insert the cardboard flap with the skewers sticking out of it into the box by pushing the skewers into the two holes you poked earlier in the sides of the box. This will create the false bottom, which should give the illusion of creating an empty box. Then, push the two cardboard circles onto the ends of the skewers outside the box, which should able to rotate without opening the false bottom. After that, your box is complete, and ready to store anything! To make it more secure, you can add digits to the cardboard circles on the outside and an arrow above the circle to indicate a safe-opening mechanism. Of course, the correct number would be the one that aligns the cardboard circle with the slits being horizontal. To open, simply turn the dial, on the side where you cut out a circle, to the number that aligns the slits horizontally, and insert the key into the slits. Then, turn counter-clockwise until the false bottom opens. To lock, simply press down the false bottom from the inside and turn the dial to some other number. Remember, the dial on the side where you did not actually cut a circle does not actually open the box, but is rather to add confusion. Have fun!

Cardboard Speed Challenge

Participated in the
Cardboard Speed Challenge