Some of the most iconic things my wife and I saw at the Special Effects 2 exhibit at the Chicago Museum of Science and Industry back in 1996 were the movie matte paintings. Long before CGI was affordable, movie special effect wizards used matte paintings to fool audiences. Matte paintings are highly detailed paintings typically done on glass with spots cut out of them. Cameras then shoot through the matte paintings with the actors behind them to give the illusion of depths, or placed in front of them either using a projector or a green screen for sets that were too expensive of impossible to build.
I’m sure you all recognize this one from the Wizard of Oz. As you can see, there is a section missing in the middle where the actors actually walked down a yellow brick road. Everything else in that shot is actually a painting.
Here’s another iconic location that only existed on glass.
That is, of course, the reactor shaft that Darth Vader ultimately throws the Emperor in to at the end of Return of the Jedi.
Matte paintings are still used today, although by and large they have been replaced by computer graphics.