Instead of an inner world of feelings, like Fi, an inner world of structured logic, like Ti, and an inner world of memories and past sensory sensations, like Si, Ni is an inner world of ideas. It's impossible to describe because it doesn't exist; it's to abstract and imprecise, sometimes to a point it's even annoying. The only way one could find out if they use Ni is by understanding how it acts and how it happens in real life. The hard thing is that, even this way, understanding Ni is very, very hard.
I'd say both Lynch and Tarkovsky have attempted to describe Ni. However, as an introvert function, Ni is still extremely subjective and personal.
All I can say as a Ni-dom is that I "absorb" the outer world without even realizing how and getting """"""""vibes"""""""" is part of my everyday life. I'm constantly processing information without even knowing it. Oh, and most Ni users have a clear "vision" of how they believe/want something will work out.