how do you get passed the seceret door in the temple district sewers that leads to the mind flayers?

<font color="gold">SOME SPOILERS
*
*
*
*
*
*
*
*
*
*
*
Have you done the Firkragg-quest? Do you remember the room where Garrens child was imprisoned? Where you fought Tazok, Chieftain DigDag etc?
Well, among Tazoks loot, there was a key named Chapel Key or something. And think that key opens the door.</font>


see ya!

Spoilers:
.
.
.
.
.
.
.
.
.
.
.

I thought the key that opened that was called the Sewer Key, and that you get it from those not-so-trustworthy group of adventurers.

I'm pretty sure about the name but NOT about the last part.

Micah and Exxon both got half of it. It's called the Sewer Key, and it's found on Tazok's body. There is absolutely no use to the "Chapel Key", which is also found in that dungeon (just to the south of Samia's party)