This quest is a simple War Table mission which can be acquired from the Ferelden side. The operation becomes available once you reach Skyhold in the main story.
Note: Once you commit to entering the Deep Roads you will be thrust into the story after a brief introduction from Scout Harding. Be sure to take the party members that you intend to use in battle and be prepared to get stuck into the content from there.
This guide for Dragon Age: Inquisition offers a detailed walkthrough of the main story and all side quests associated with each region, detailing easily missed features and hidden lore secrets along the way. The guide also covers all three main DLC: Jaws of Hakkon, The Descent, and Trespasser, and all dialogue choices throughout the game.
Inside this guide you will find:
Coming Soon! A detailed Character Builds section with coverage of all classes, skill trees, recommended armor, weapons, consumables, and much more!
A Walkthrough for all main story quests, detailing the consequences of your choices along the way.