Difficult movies suggestions?

You know how sometimes you feel like reading a difficult book, just hunker down and let your mind work at it?

Do you have any suggestions for movies like that?

I'm looking for stuff like Primer, Lynch movies, Holy Motors, NOT movies that are difficult to watch only because they are extremely gory or disturbing in some straight forward way. (There are plenty of those "extreme movies" lists to find with just a search.)

You might want to check out:
Beyond the Black Rainbow

Oh, thank you. I heard of it before, but the reviews were mixed, so I haven't watched it. Added to watchlist.

You could try Shoah.

Enemy (2013)

Maybe these?

Upstream Color (same director as Primer)
Tinker Tailor Soldier Spy
Timecrimes

Ones I haven't seen but heard good things about:

Mr. Nobody
The Mirror