The majority of the actors (with the exception of Hias and the glass blowers) were actually hypnotized by Werner Herzog and perform under hypnosis on screen.
The main character "Hias" is based on the legendary Bavarian prophet Mühlhiasl.
The final scene was shot at the same location in Ireland's Skellig Islands as the Ahch-To sequences in Star Wars: The Last Jedi.
In a New Musical Express interview from May 1979 Deborah Harry mentions Mike Chapman naming Blondie's 1978 song "Heart of Glass" (which he produced) after this movie.
Werner Herzog: one of the men carrying a load of ruby glass on his back to be thrown into the river.