Note: If you don't want to play through Awakening a second time, make an extra save after completing the third story quest.
After the third story quest is completed, Amaranthine will be attacked. Head there and you'll be given a choice to make, continue saving Amaranthine or save Vigil's Keep. Choose to save Amaranthine. Fight through the city saving the city's guards. After all are saved, head into the Chantry until you're told that the Darkspawn are attacking again. Go to the Crown & Lion Inn and fight the Darkspawn. Go through the secret door in the back into the Smuggler's Cove and continue the fight. Return to the surface to face another Darkspawn general and a new opponent, the Armored Alpha Ogre. Both are just beefed up versions of their previous versions.