It appears you missed a few steps...
Take the Masque of Evil to Shururgeon Castle...you'll need it there.
Completing the Castle will give you clues as to what happened and what to do at Dragon Spire. This will in turn open the exit out of the Spire to the way to Brimloch Roon
Additionally, the Stout Mines would have helped you getting through Dragon Spire...although it appears you have gotten by that problem already.
It is possible to climb that wall and bypass Dragon Spire, but as that's where you get the Mavin (shameless spoiler there), its only real benefit is in cutting down on travel time going from Ishad N'ha to Brimloch Roon without using teleport spells.
|