I am starting this thread so that you all will discuss about the most ambitious film projects ever, whether they are live action or animated.
To start with, I will like to share a very ambitious movie project: Peter Jackson's The Lord of the Rings film trilogy:

The reasons why it is a very ambitious movie project:
A) Making 3 movies at once, or back-to-back
B) Filming an unfilmable book that had both fans and haters
C) 0 big name stars
D) special effects that are still being created when all 3 movies are being made
E) Director who is mainly known for low-budget horror movies (i.e., Peter Jackson, who lived in New Zealand which is halfway around the globe from where I was living)
F) pressure from a studio (i.e., Miramax) to condense the story into one or two movies
and much, much more.
Are there any other movies, animated or live action that qualifies as some of the most ambitious movie projects ever?