There is a lever for the door to th etreasure room with the dragonrider. It is west of the room where you meet with the other "big shot" in this dungeon.
Zandalor is captured in the treasure room of stormfist castle. You first have to go inside the castle and do the jobs, exit Iona's dungeon and then you can go and rescue him. You have to get the secret entrance from the guy in the ducal inn in Verdistis (thiefs guild boss, cant remeber his name).
