https://en.wikipedia.org/wiki/List_of_films_with_longest_production_time
interesting reading about the various complications for many of these films
I love reading up on that stuff too.
- The Act of Killing: This is near the top of my list of things to watch next, heard it's fantastic
- Avatar 2: "writing and visual effects prep work happening simultaneously for seven years" Did we learn nothing from the Star Wars prequels?
- Begotten: Still need to see this one
- Boyhood: IT TOOK TWELVE YEARS TO MAKE
- Eraserhead: One of the best examples <3
- Evangelion: 3.0+1.0 Thrice Upon a Time:

Was surprised to see this here but it's true.
- Movie 43: How much behind the scenes info is there on this one? Lol
- The Thief and the Cobbler: The documentary on its making, Persistence of Vision, is really good