I've had a few quest lines on the side that were broken but I thought the main quest line would be solid.

I have went to the throat of the world, talked to Paarthurnax and then went and talked to Septimus.
I have two quests:

Elder Knowledge - Recover the Elder Scroll (since I know the location)
Descerning the Transmundane - Transcribe the Lexicon

I am in Black Reach behind the city - and the whole area is "not drawn" - its like the actual area is invisible. So I used the Clairaudience which walked me a path to the tower of Mzark. I actually walked through midair here - I am guessing there is a bridge that is invisible to the tower.

Now that I am there - i have both arrows in front of me "Transcibe the Lexicon" and "Tower of Mzark" Recover the Elder Scroll
I got a "Open door" - which I opened - now it says (A) Close Door

But it wont let me in.
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Id show you a picture but there just nothing in front of me but open space.
This seriously seriously svcks.

After saving the game and reloading - the problem went away.

Here is the deal though - you have to use Clairvoyance to follow the path through mid air to get to the tower -
Once you are there - save the game and exit
Reload the game and the entire corner of the map will render - the tower, waterfalls, everything.

After another reload the corner disappeared on me along with the Tower but during the game it loaded - I played everything that was there and finished the quest.

Something is wrong.

I walkewd on a solid standard dwemer walkway all the way into the tower.

Something is wrong if you are walking on air and Blackreach is not appearing properly.

ya that is weird when I went everything loaded up just fine. Maybe it was caused by the cache build up an it didnt render the area for you.

Definately was weird. First time I went there - the arrows were there telling me to go that way but there was no terrain to see or anything. My character was interacting with the environment as if it was there but I could GET up to the tower. Afterwards, I figured out it was because I was below the bridge... when I use clairaudience to show me the path to the door - it led me over the bridge that wasnt there. when I got there and opened the door. I still couldnt see anything. So I saved the game to find a solution. However, the next time I loaded - it loaded correct and first I thought it loaded the wrong save - since I expected to be in thin air.... but everything was fine after that.

I can reproduce it by loading an earlier save and walking over there - still thin air - however, any save AFTER I went to the tower - loads the tower just fine.

I literally have the same problem

How did you get passed? No matter how many times I play it won't load it completely

I dont know what to do

What I did was use the Clairaudience spell and followed the path to the door of the tower.
Atter I got to the tower - I opened the door but it wouldnt let me go in

So I saved the game and shut off the xbox 360 and came back the next day
When it loaded from where I left off - it loaded the tower correctly. The first time I did it - it didnt load correctly but that was the same day.
The next day when I loaded - it was a miracle and worked.