[color:"orange"]I haven't got any quest info in my quest book about Zandalor's Rescue as the only time I heard about his whereabouts was when I was in the castle and they wont let me leave.[/color]
Did you reload an earlier save, or find some other way to get out of the castle? If you talk to Janus and do a few quests for him, you will be able to leave the castle (loot the place before finishing the quests). After that you end up in Iona's dungeon, and upon exiting you are given the quest to rescue Zandalor. Until you have the quest, the door in the sewer treasure room entrance will remain locked.
By joining the thieves' guild you can get access to the poor quarter sewer entrance (in Lain's house) and the treasure room entrance will be flagged, but that is it.
