I think I can build a career making cardboard toys. Every time my daughter has an "idea" for a toy, I have get ready to build something out of cardboard. After the doll house, disk drop game and rolling ball machine, the latest idea from my daughter was to build a periscope. She probably saw some youtube video of some one building it.
The idea was to make a hollow rectangular cylinder and attach two small mirrors on the ends at 45 degrees. We bought some mirror toys from the local stores for this purpose. Then removed two mirrors out of them like you see in the picture below.
I cut out a rectangular cardboard to be rolled into a cylinder. Then, I made a housing for the small mirrors, attached them at 45 degrees using hot glue.
After testing out the periscope, my daughter had a lot of fun playing with it. She would hide behind walls and snoop on people in other rooms using the periscope. Not sure how long the cardboard device will last, but she certainly is having fun :).