Leave the house of Khan Ti Kah's daughter and check the illuminated cave on the left. See the sculpture on the pedestal and snatch the Yukol lense 01, which is installed roughly at its center.
Get out and proceed down the path back to where we began. Now you can take the gate to the left, then proceed towards the bottom of the screen and to the right in order to reach the Yukol camp. Talk to Kurk, who's standing more or less where you've stood before (closer to the bonfire) and give him the manuscript. He will give you back a translation. Read it closely (via equipment) - you will learn that one of the Yukol keys can be found within on of the idol of idleness.
Proceed towards the brick building (top of the screen) and now enter the open gate. Directly behind it, go to the stairs on the right (shown above). You will enter the bulding.
From the top of the stairs go left, and when the perspective changes, go to the right, via the corridor with red carped and a glass wall - take the first left, and enter the door at the end (shown above).
In the room that you enter, look at the display case - right next to the door. Crack the window in zoom - use the Sara's scarf from your equipment to protect Kate's arm. Take the Yukol lense 03.
Get outside and continue walking down the corridor with the glass wall. When the perspective changes, go to the left and go down the first staircase you see.
Opening the safe in the Yukol chair
You'll find yourself on a landing above the wide stairs. In front of a pile of rubble there, stands a quaint chair. Zoom in on it, and open the cover below its seat with your mouse.
You will se a sort of a cipher lock. There are six entries here - each with a Yukol symbol on it. The clue can be found in the manuscript; the symbols signify ghosts: sacrifice, pain, death, mourning and madness. As you can see, there are only five symbols in the manuscript; one of them is doubled in the combination. Each dial in the lock has only one genuine Yukol symbol - the remaining ones are fake, so the task is to recognize the Yukol symbols. The only exception is number 4, which contains two genuine symbols.
To break it down: turn each dile (with the mouse). The first one should be the ghost of sacrifice. Then comes pain, death, sacrifice again, mourning, and madness. The right combination is shown above.
Getting the combination right will let you rise the seat of the chair (with mouse of course) - from the cache, pick up the last Yukol lense (02).