Look at the image in the periscope eyepiece. You can turn the device around its vertical axis. What can you see?
How it works
Thanks to a system of precisely set mirrors which reflect light rays, your eyes receive images of places that cannot be seen directly (see the figure).
Periscopes with more complicated optical systems are used in military vessels and vehicles, e.g., in submarines, tanks, armoured cars. Currently, they are being superseded by video cameras.