When I saw Return of the Jedi in the movie theater back in 1983 I and everyone else thought this matte painting of a Rebel hangar was a real thing—that, somehow, they managed to build a full size set with giant models. It was all a magic trick that used distraction to fool your brain. This BBC documentary explains how.
The Return of the Jedi part starts on the 3:32 mark but I recommend watching the entire thing.