Yolo sent you a dream informing you that she saw Ventrix in a cavern that look like a maze with battlements on the maze walls. Korrigan your Duergar guide tells you that this is part of the outer works of defense for the Duergar city of Khazaldum known as “The Dead Slots”. It’s a very distinctive area. He sketches out a map to show its relationship to where you are.
Yolo reported that Ventrix does seem to be traveling with a mixed group of additional companions now- some duergar, an ogre, and some others she did not get a good look at.
You can find this map on the roll20 site. The current page should be the map. Squares are 10 miles across. The map is Korrigan’s sketch and is not precise, nor does it show every last passage; there are many smaller ones.
Your location is the red, eight pointed star. Marselene has shared some information on the temple.