Most of the fjords will be blocked off with a barrier (which can not be disabled until you take over the battle tower). There should also be stuff left to do in Broken Valley.
When you defeated Amdusias, a barrier blocking off one of the corridors there was lowered (opposite the chamber with the bedrooms upstairs), which leads to a teleporter which will bring you to Sentinel Island. Your first encounter there you can mindread to go up a level, so the higher level you are the more of an experience bonus that will be. I made it to 22 in the fjords, with Broken Valley pretty much cleared (only a few quests left to turn in). You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus (equip anything you have with a Wisdom boost).
