Aaaand... it appears I encountered a game-breaking bug and am stuck for good. Unless I'm dumb. But I don't think I am. Because I can't figure out where things went wrong, I'll describe what I did.
I'm in the last dungeon and had/have to find two gold keys. Because I couldn't figure out the lever puzzle in the left building, I went to the right one first and got a normal key. Didn't see the door because I'm blind, so I took the normal key to the normal lock in the left building and fought the three dragons. The game told me I got a gold key from them, I teleported out and went back to the lever puzzle. I figured it out and freed two elves but couldn't find the third one, so I took a break, saved and closed the game.
I tried again a few hours later and then found the last of the elves being invisible by the pond in the entrance area (another bug?) by helplessly running around and trying to examine things and so got the next normal key, which I took to the building on the right. Unlocked the door, fought Horror, used the grass circle, got the chest with the second golden key.
Except when I went to the door with the golden lock, the game still told me I need two keys. Checking my inventory, it says I only have one. =/ My guess is that I maybe never had the one from the dragons or "lost" it because while looking around for elves I went back to the dragon fighting spot, went to the screen south of it and when I wanted to go up again the game asked me again if I want to save and then proceed even though the dragons were dead. The fight didn't trigger again or anything, there's the teleport spot there and that's that. But yeah, I should have two golden keys but only have one and am therefore 100% stuck and unable to proceed. Reloading didn't help.
Any help? What do I do now?