I was doing the quest for Arniel to reconstruct keening and I was searching for the lost courier. I'm pretty sure the courier's location is radiant based but I was in a castle searching for his body. The castle was full of mages and as I was exploring I heard sounds of battle far off. When I finally found the source of the sound I found several mages battling a daedra. Thinking nothing of it i proceeded to kill the mages and prepare to fight the daedra. upon examination I found that the daedra was actually Sanguine! From what I can tell, his magic grove or whatever is placed above this keep and is invisible. Somehow he slipped into this keep. There was also a small section of the keep that I couldn't approach as it would teleport me to his grove and I wouldn't be able to escape. I play on xbox so this wasn't a mod. Anyone else experienced something like this?