There are a couple low areas to the east and west just as you enter the channel south of the harbour and slayer camp (at the edge of the anti-dragon shield). If you keep going south there is a cave on the left, near a crashed zeppelin in the water.
There are a couple caves near the start of the fjords (one left of the bunker, another near the source of the waterfall across from the grand knight teleporter shrine) and further in.
Did you finish off the well cave in High Hall? At least on nightmare I found clearing the final section quite challenging on level 34, though on level 25 I could have just killed the boss and left (I reloaded instead, to see if a higher level would let me take out everyone).
Stone's flying fortress is the easiest (teleporter on the north east end of the island across from the dragon cliff castle), followed by Raze (mountain across from the harbour), Broken Valley, Keara and then Kali (Rivertown Gorge).
There is no rush on helping Zandalor; the quest there doesn't need to be done until you are ready to head to the Hall of Echoes (though you may be a high enough level it wouldn't be too difficult).
You are past some of this already, but:
next lvling area to go to.
