If you had finished all quests in sentinel island as you claimed, you should have met and save a guy name elfrith, which he hide on top of some stone pillars, where he being surrounded by a group of dragon elves. Upon saving him, he will give you a spell book. Sassan's grave should be mark in your map, which is in the northern part of sentinel island. Use that spell book at sassan's grave and light the 3 sets of candles that surrounding the grave. You can then proceed forward on the quest. It has nothing to do with orabas fjords area for getting your battle tower.
