no no, you all have the wrong idea (my bad explination.. sorry)
I have gone through the keep of tinrya, and after traveling through the whole thing you come out on the other side of the keep, in a pool of lava, the pool is surrounded by cliffs, you have to go somewhere from the pool of lava (aka north) but in order to head north, you need to fly over the cliffs
(i am not trying to skip anything, this is the natural walkthrough of the game)