This is another along the main quest. You'll be asked to go and speak to Mervis in Amaranthine about merchant caravans disappearing. He'll direct you to the Wending Wood. After exploring, you'll meet Velanna. She will tell you who is behind the caravan attacks. Find the sole militia survivor after that. After encountering Velanna again, head to the Darkspawn Camp and then head into the Silverite Mine. Once inside, you'll see The Architect for the first time. You'll be imprisoned and all of your items will be taken away. After escaping from your cell, you'll have to fight, but without your weapons and armor. Pick up what you can on the way. Each character's equipment will be worn by an "Experimental Subject". Kill them to get your gear back. After you have all of it, your final fight will be against two dragon thralls. After a few hits, they'll both fly to another spot in the room.