"Find the Raiders' hideout" is a mission objective in Sequence 13 / Memory 05: Under Lock and Key
Walkthrough[edit]
Head to the North and make your way over to the marked Underground entrance in the Cemetery District. Slip in and head on down the stairs. You are back in the Catacombs. Head across the beams to the North and take up a cover position to the right of the door. Wait for the Raider to come over and get him with an assassination. This should scare off the other two nearby Raiders.
Down down to the ground and head over to the West. This will lead to a massive cavern. This is the Raiders' Hideout.