In this activity from Fetch! learn how to make a periscope so you can peer over walls and peek around corners. Periscopes work by directing light in different directions with mirrors. One mirror reflects light to another mirror. That second mirror directs light to your eye. In that way, you can see things that are not in your direct line of sight. Submarine crews, soldiers, and surgeons all use periscopes or equipment that works like a periscope.