Awakening is a main story quest in Skyrim: Dawnguard.
The quest Awakening starts inside Fort Dawnguard
I've met Isran, the leader of a group of vampire hunters known as the Dawnguard. The vampires that attacked the Hall of the Vigilants may have been after something in a place called Dimhollow Crypt. Isran has asked me to find what the vampires are looking for.
Find out what the vampires are seeking
Speak to the mysterious woman.
Kill the enemy vampires inside
Enter Dimhollow Cavern
Solve the Brazier Puzzle by pushing all braziers into a hole such that purple smoke comes out of every Brazier
Talk to Serana
Dawnguard, where you learn about the vampire hunters and travel to Fort Dawnguard