Just beyond Southfringe Sactum there is a gate that does not open but if you climb the wall to the right, you get to the path on the otherside.
Continue through the mist and in the distance there is a white tower, i haven't been able to reach it as at some point i fall through the floor and end up in water, once in the water you can't get back on to land.
So what is the white tower ?

You could mean White-Gold in Cyrodiil. It's as a bitmap in the game.

i think it was suppose to see it from the Throat of the World, but maybe they failed to do it, annyways, Vvardenfell is there too, and the Red Mountain is the "DRAGONBORN" dlc so maybe we will have the white Gold tower in the Future, since we maybe can travel in a dragon

Edit: spotted an gramatic error, i writted: " so maybe we will the the" when it was suppose to be "have the" sorry my bad corrected

Fingers crossed eh?

Sounds like a plan sir, now let's hope we didn't jinx it.

No, Dragonborn is on Solstheim (sp?), the island to the north of Morrowind and Vvardenfell. In any case, Red Mountain and almost all of Vvardenfell is a volcanic wasteland now.

Solstheim is correct.
I think he reffered to Red Mountain being visible from Solstheim in the DLC.

I had read that it could be seen by disabling boundaries in settings on the PC but im playing on the XBOX.
So just head to Southfringe Sanctum and keeping the sanctum on your left go over the brow and as you get past the rock look up the hill and you will see the gate. (best go on a horse as it is some distance when you get around the gate)

Go to the right of the gate and jump up onto the rock and down the otherside back on to the path, follow the path around the bend then keep left and you will see the tower

yup