This one was interesting - I'd have taken pictures if I knew it was going to turn out like this. It's the second-to-last Thieves' Guild quest where you have to enter those ruins where Mercer is looking for the eyes. Outside the ruins you have to work your way up to the door to get in. Well, I get there and I'm working my way up and I can see the door but absolutely no way of reaching it. I try going all the way back around, climbing the mountain, and dropping in from above, no good there as the top of the doorway is flush enough with the bottom that you can't swing back in before passing it.

I finally surrender and try using Clairvoyance (I avoid using that spell as much as possible as I like to try and find my own way to things in this world) and as I follow the path up towards the entrance to the ruins it suddenly just goes out over open air, up to the roof of a gazebo-type-central-area-thing, and then up through the air again to the ruins entrance. I spend about 20 minutes looking for some switch to active a walkway in the area, no luck there, so I think maybe there's just an invisible path. I figure it's a long walk back up if I'm wrong, so I save right at the edge of this "invisbile" walkway and then try to go out on it. Sure enough I plummet to the ground. I reload that save and BAM there's two walkways that were just flat out missing before exactly where the Clairvoyance vapors were pointing.

It's just funny to me that those were the exact two pieces of geometry that were missing from that area - just about anything else and I might never have known something was wrong at all. Makes me wonder how much stuff hasn't loaded that I haven't noticed, but at least now I know next time something seems to be missing maybe I should just try the "save/load" spell and see if that fixes it.