Arguably the most important film never made, Jodorowsky's Dune has influenced an entire generation of movie makers despite being never shot. Jodorowksy has HR Giger, Chris Foss and Mobius on design, Pink Floyd on music, Mick Jagger, David Carradine, Udo Kier, and Orson Welles in the cast and even secured Salvador Dali to play the Emperor (Dali refused to read the script and wanted $100k/hour to appear). Jodorowsky wanted to make the film 10-12 hours long, and that's what he pitched. A multi-million sci-fi epic like nothing which had ever been made before. So obviously, nobody funded it.

However, he did make his handbook, The Dune Bible, (link goes to the most complete archive I've seen of scans/captures from the book) of which two known copies still exist. A lot of the design work made it into Lynch's film. Other directors have seen the book too, including, I'm sure, Denis Villeneueve who will hopefully be taking some pointers while making his film.

1917 editor Lee Smith reveals the truth about Sam Mendes' one-shot film

This is my favourite passage from this article:

He asked [a journalist] how long the film shoot was; she looked at her notes, said four months. How many days a week? Five.

Do you think they never turned the camera off, he said; just do the maths. "And she went, 'Oh, right'."