You’ll need a Flame Butteryfly to open a small location that holds the Garrison Ward Key.
Darks Souls 2 guide: Crown of the Ivory King – Garrison Ward Key
You need to light the four pedestals here using a Flame Butterfly, which will open the big door. You can’t light the pedestals until the ice has been thawed.
If you don’t have a Flame Butterfly you should go back to the room with the doors on either end where you killed three Frozen Soldiers and a Frozen Hound. Through the door on the far right is a lit pedestal where you can light a torch. If you don’t have a torch you need to kill the prisoner in the opposite building to where the Frozen Eleum Loyce, Abandoned Dwelling Bonfire is found. When the ice has thawed, the enemy drops the torch.
Go through the doorway when it opens and you’ll see seven Retainers along the inside wall. You can use ranged attacks to take them down as they drop and approach you. On the left on the rock wall you’ll see the outline of a door – examine it to find a hidden path, which you should follow. Follow the path left to find a Bone First weapon.
Now go back down the path and straight ahead in the adjacent passage to fight the Flexile Sentry.
Once the Flexile Sentry is dead, go up the left passage. Looking down you can see another Flexile Sentry in an alcove below you. It’s easy to kill from here with a ranged weapon.
Pick up the two Human Effigy items to the left of the passage you just came out of and drop down to pick up the Garrison Ward Key that the Sentry was guarding.