You've collected the Garrison Ward Key from the Garrison Ward Key cave. Now it's time to use it.
Begin at the Abandoned Dwelling bonfire and follow the only path forward. Keep in mind the road ahead will include the old enemies you fought plus five Retainers peppered around the area. Stick to the strategy you used before, creating separation between you and your enemies and fighting them one at a time.
When you reach the intersection after fighting the Crystal Golem on the bridge, turn right, head up the steps and kill the Crystal Sorcerer in the room and the Retainer who'll follow you in.
The treasure chests in the room are no longer encased in ice, so help yourself to their contents. The rightmost is a Mimic, so kill it. Pillage the remaining chests for Titanite Slab x 1, Old Radiant Lifegem x 7, Bonfire Aesthetic x 3 and Brightbug x 2.
Leave the room and head straight down the short staircase, killing the the three Hollows and the Crystal Golem. Interact with the door at the end of the path, which will now open because you have the Garrison Ward Key.
Light the Expulsion Chamber bonfire.