24 - 3"x5" index cards, 2 - mirrors about 3" by 3", tape (scotch and/or masking), scissors
Procedure
Begin by laying out index cards in a grid of 4 by 2.
Tape all the edges to join all the cards together.
Fold into a square and tape together, so that you have a square tube.
Cut out shaded sections.
You now have the center section and the basic structure of the periscope. Next, we will build additional pieces to direct the viewing area.
Lay out index cards as shown below.
Build this piece twice.
Cut out the shaded area, and tape together all the edges to form a square tube.
Now you can join together the 3 sections by matching up the openings in the sections so that they are joined perpendicularly (below).
Place the mirrors at the joints at a 45 degree angle.
You should be able to see objects on the other side of the periscope.
Adjust mirrors if necessary.
Tape the mirrors so that they don't fall out.