From the Altar, follow the yellow board sign in the northeast direction. Open the big gate with Iron Insignia Key, climb the stairs.
Side Story: Otto’s Mill – Take a left at the junction, before the stairs.
Cannibal’s Plunder Treasure
When you reach the Forbidden Woods, deals with all the Lycans who show up
STRONGHOLD DOOR
Continue up the hill and into the ruins. Take the ramp on the right (south) wall, and follow it around anti-clockwise. Dealing with the Lycans as they appear.
At the top, head to the door on the east wall. Climb up the ladder in the northeast corner and pull the lever. Deal with a group of Lycans. Jump below and reach the other side via stairs to pull the second lever.