When I first learned about this device, it was called a "Pinhole Microscope." I don't think it has enough magnification to be considered a microscope, so I'm just calling it a magnifier.

Materials:

Clear beverage bottle (a half-liter water bottle in this case)

Dark, opaque plastic piece, large enough to cover the top ot the bottle. (top from a peanut can) Cardboard, like from a cracker box, will also work.

Tools:

Knife, scissors, or both (Okay, I'm using tin snips. They were easier to find!)
CA cement (Superglue, Crazy Glue or the equivalent)
Pin (not shown)
Sandpaper (not shown)

Step 1: Cut the Bottle

Cut the neck off the bottle just below where it starts to widen. This should give you a section about 1" (25mm) long. Sand the cut edge smooth, so nobody cuts themselves on it.

Step 2: Cut the Disk

Cut a circular piece of your opaque material, just large enough to cover the top of the bottle.

Step 3: Glue

Glue the material over the top of the bottle. You may want to roughen the bottle top a bit with the sandpaper first.

Once the glue is dry, poke your pinhole in the center of the opaque material. Start small, it's a lot easier to make the hole larger than it is to try to make it smaller.