I’m looking for a series intimidatingly large (volume-wise) and long-spanning fantasy books, preferably non-SF (unless it’s a kick-a$$ space opera alike the Mass Effect video game)

I'd appreciate if it got progressively more dark, gritty and depressing as the story progresses. I'm speaking stuff like SoIaF, Harry Potter, LotR in scale. Also preferably from a lesser-known author (at least to a layman; I suppose there are no lesser known authors in this sub…). Bonus points, if it came out in the 20th century.

PS I'm in my late 20s and like to think of myself still as a young adult, however I found most YA media unlikable and that was already a few years ago when I still read a lot… :/