Bicycle and car reflector
The red plastic reflector on the back of a bicycle or a car is shaped so that light from a car’s headlight passes straight through the front surface.
The back of the plastic reflector is shaped like a row of 90o prisms.
Total internal reflection occurs.
All the light bounces back and is returned in the direction from which it came.
No matter in which direction the light is incident on the reflector, it always retraces its path.
So, car drivers see the reflection of their own headlights in the reflector.
Periscope
Two 45o prisms can be used to make as a periscope.