After navigating through the maze and obtaining the EASTERN SHAFT KEY, as described in the main walkthrough, return to the north end of the maze, exit through the same gate where you entered, and climb the ladder to get back to the desert.

Exit the small pyramid and head to the right, toward the excavation pit.

Take a running jump across the pit (to the east side). You're aiming for the square ledge on the other side a little to the left. Turn left (north) and take a running jump to the next ledge.

Now take a standing jump up to the next flat block, where you'll need to kill a giant beetle. You may want to use the revolver here if you have ammo, since the beetle can knock Lara off the edge if she doesn't kill it quickly.

Climb up two tiers on the side of the pyramid.

Then take a diagonal standing jump to the next flat spot above and to the left (north).

Take another diagonal standing jump to the next flat ledge above and to the left.

Wait for several falling blocks to tumble down before moving to the far (north) end of this ledge.

From there, take another standing jump to the next flat ledge above and to the left...

...and Kill the 2 giant beetles that fly out of the doorway.

Finally, climb to the doorway and use the GUARD'S KEYS (which should still be in your inventory from previous levels) in the keyhole on the left to open the door. Enter the pyramid to finish the level.

[Khufu's Queen's Pyramids Walkthrough]