There are 5 (I think) flying fortresses, though Stone is one of the biggest. There are actually 4 bosses in Stone. 3 mini-bosses and Stone himself. Like I said, look for teleporters. You can even take off dragon form right on top top of the teleporters and go right into them without taking much damage.
Be warned though, if you do that you might have to go to your tower and use the shrine to get out, as you will be in the middle of a lot of angry Black Ring when you come back out of the teleporter and there won't be enough room to instantly change into your dragon form.
