The Hall of Echoes is the end section of the game, so finish off everything else first (from the dragon sections you can get back to the battle tower, but not leave to go anywhere else, besides back to the Hall of Echoes).
Head to High Hall to find the Drudanae.
Talk to and/or mindread the merchant.
The quest to free Orobas is relatively short (you may want to save before entering, though), if that makes a difference in what you want to do first, that or the flying fortress in Rivertown Gorge.
