Here is a no commentary full playthroigh to obtaining the secret of the queen mother achievement. It picks up directly from obtaining Sanctuary of the Guardians.
You are tasked with gathering 4 stelae for nawal, the first is in a pit to your left, burn the spider webs at the bottom to access the chamber were it is hidden.
Once out of the pit, head towards the Great pyramid and just past the Sphinx you will find Omar in a tent on the edge of a dig, speaking to him will start a cut scene and the secret of queen mother quest.
Head into a dig being careful of guards, you can use stealth or dispatch them without raising attention. There is a zip line that will take you close and you will find an elevator in need of power.
To power the elevator, you will need to the follow the red and blue wires to a switch, I followed blue first.
Head up the stairs, there are a few enemies to avoid or take out here so get past them with raising an alert (I knocked most out or pushed them off ledges). After the first you cam drop down and find a secret artifact before heading over a ledge into water and through an underwater entrance.
This will bring you to another room with weapons to take our the guards, I dropped behind the first, there is also a book here for the button man in an unlocked chest.
Head past the wheel barrow and up the ladder, there is a guard you can push off and flick the switch.
There is an exit to the lift and you can now follow the red cable.
Another room with guards but there are plenty of melee tools, I used them to take a few out. You need to climb higher before swinging across to progress.
Another guard is here but you can easily drop behind by going through the small gap, here you will find the lever you require to power the elevator.
Once powered, you can go back to the elevator and pull the lever to bring it up, enter and hit the button to descend into the shift.
You will find a mural puzzle, the tomb of the queen mother. You need to enter 3 glyph to solve.
The fist is next to the puzzle, it's a bird that goes in the top.
The second is towards the back, a fish that goes in the bottom and in the centre is a snake that goes in the middle.
Grab the sledgehammer from the wheelbarrow, as there is a breakable wall at the back that the light now shines towards
Here you will find the secret of the queen mother, some nazis will come into the chamber as you exit but you can sneak past the back to the elevator.
Now head back up, back to omar and you will unlock the achievement.