Dutch documentary The Making of the Empire Strikes Back never saw a commercial release but contains a fascinating and rare glimpse behind the scenes of the beloved film. The language quickly switches to English, which is convenient, but you'll have to bear with the shoddy quality (it's worth it). Part Two is here.
Michel Parbot filmed a lot of behind-the-scenes footage and interviews during the filming of The Empire Strikes Back. Some of it was used in a French documentary, while the rest ended up on Dutch TV. The French documentary was included in the Star Wars blu-ray release, while the Dutch footage has only been seen in a few very short low quality clips on the internet.
Now Star Wars Archives has uploaded an almost complete version of the Dutch TV special in a much more watchable quality.