OK, i need to rescue the bard NPC from the evil mage in the sewers. I know it's in the temple distcrict sewers but i've already gone all through there for the unseeing eye cult mission.

i found a secret room that consists of 3 large circular rooms with a bunch of baddies in them. I though i was on the right pace untill i reached hte third (has a podeum in the center). There's nothing in there!

Look for more doors in the Sewers.

NOTHING in there? Better look harder.

Hey, congrats! You just blundered your way through the Hidden! Be sure to pick up the Hammer of Thunderbolts before you leave to go check the northern walls of the sewers.

"The Hidden"???

Look in the podium you described.. You fought mind flayers at this place, did you not? There's a container with some good loot and a letter which should explain everything.. almost.