I cannot find my original notes on this game treasure, so I’ll type up another list.
The cistern on level 6 lets down into the long cavern passage. It would be easy for the character party to miss the secret door. The hole in the floor on room 161 on level 9 lets down into the treasure room.
The exit does narrow. It becomes a nondescript opening in the ridge, on the south side of the ridge towards Quasqueton.
Strazl Deathlcaw is responsible for a number of disappearances over the years. One of the rooms, 214, in the cistern down from level 6 room 101 has a teleport area that leads to room JJ under Fall Keep, in Fondfield, Trillolara. That room under Falla Keep is a Gashtran spy nest and was discovered in a separate adventure.
The Chaotic Evil spy nest grabbed victim’s for Strazel to torment. In exchange, he let them have the teleport room here, and didn’t kill them.