I have the same problem with the Keep.
When I try enter the "kitchen" area, or go in with the big main door I just get a blackscreen.
Posted this on reddit also, here is the text from that, with some more info about what I tried.
"Hello, first of all I just want to say I love the game.
Now to my problem, I'm working on the quest to take down Raedric, I have more or less cleared all of the castle. I started by climbing the side of the wall, killed most stuff, entered the temple/priest part, then went down to the kitchen, there I got stuck by the big door didn't have key/mechanics enuff. I went outside and killed some more stuff, I then found the 2nd way in with the sewer, I chose to kill the "Necromancer" down there and couldnt open the big door down there (not sure if I missed the key, or if that's the way you get in, if you help her).
Anyway at this point I thought that I should return to the kitchen area since I saw that I had a big key in my questitems, and also it's the area that I might have missed something in.
Now for the problem, when I click on the staircase down to the kitchen I first get the loadingscreen then everything goes black, I get the cursor but its the red "stop" sign, I can move it around but it's just black, if I do any mouseclick I get a "windowserror" that PillarsOfEternity doesn't respond anymore.
I have no clue how to go around this.
Right now if I just press Continue (and thus load the autosave down to the kitchen) the same thing happens, I have a quicksave more or less just outside that part and if I load that the game works but if I go down, I get the same thing again.
Is this a known problem? Can I send my savefiles to some support and have them look at it?
Thanks in advance, not sure if I should just skip the quest and do other stuff, but then again I want to finish this, feels like a big quest.
EDIT: I just thought that what if I enter from the frontdoor, so I tried that and same thing happens."