An external back seat common on automobiles made in the first half of the twentieth century.
These seats are placed inside of a shallow trunk and when needed, the trunk lid can be lifted up to form the backrest while the occupant sits on the padded floor.
They are not nearly as comfortable as real seats, because you kind of have to suck your knees into your chest. However, it feels very cool to ride around on the outside of a car without any semblance of safety.