I just beat Count von Zur, but the door left of his throne room did not open.
I then left the area to the main corridor to save and stack up on ammo (I also discovered the throwing hatchet), then came back.

I noticed several times the colored doors close back and since the keys are gone I have to trek around, but I also don't see how I can open the door in the tgrone room and get the gold jey to exit the corridor.

Anyone has any idea?

Found it, my save was seemingly corrupted and some triggers were glitched, I restarted the game and everything went fine.