The group quested into Seven Pillared Hall below Thunderspire mountain. Each traveler has brought their own reasons to venture below, but all share a common goal; to learn of a deeper evil they feel is festering in the long lost Minotaur City.
The group uncovered a slave operation and routed the Bloodreaver gang in the Chamber of Eyes. During the rampage, Duergar were encountered and appear to be purchasing slaves for some foul purpose.
The Ordonator Arcanis provided the location of the Duergar Grimerzhul Clan’s stronghold: The Horned Hold. An ancient minotaur fortress of the deep, seated on the edge of cliff that falls away into an endless nothing. The Ordonator Arcanis seems intent on silencing the slaving problem causing unwanted attention to the Mages of Saruun’s stronghold trading post.
Check out the wiki. There is some more helpful info there.