Approach the deep pit to the northwest, between the GREAT PYRAMID and the two smaller pyramids.

First jump onto the small, square ledge on the left (west) side of the pit.

Take a running jump angled to the left to land in the space between the two small pyramids. Immediately turn left...

...and kill another giant scorpion that charges out of the gap between the pyramids. Take care not to hop back into the pit as you fight.

Move out onto the downward sloping ledge...

...and take a running jump across the pit to grab the block ledge on the opposite side.

Pull up, turn right, walk to the edge, and take a standing jump to the next block ledge.

Kill the giant beetle that buzzes in from above on the left.

Here it may help to turn and hop back against the wall as you shoot to avoid accidentally hopping/rolling off the ledge.

Then turn around and pull up onto the ledge where the beetle came from.

Turn left and take a running jump, without pressing Action, to land on the next ledge jutting out from the sandy slope.

Walk forward onto the far left corner of the ledge and take a standing jump over the sloping sand to the next ledge.

Turn left and take a running jump along the right side of this ledge to grab the middle or left side of the block ledge on the far side of the pit. Pull up and turn right.

There's a giant beetle sitting on the rock ledge ahead. Shoot it from here using pistols or revolver.

Now ready a more powerful weapon and take a running jump to the ledge just below the one where the beetle was. Run up the slope...

...and blow up another giant scorpion as it comes around the corner from between the pyramids. (If you don't kill the beetle first, you'll have to deal with both at the same time.)

Go between the two small pyramids, where the scorpion came from, and you'll find a small medipack lying on the ground.

There's no need to light a flare here, but if you do so, it's easier to see the faint bird symbol carved into the ground next to the medipack.

Turn around and approach the large, uneven stone block sitting nearby. Go around behind it...

...and push it onto the symbol.

This opens a concealed door in the small pyramid on the left.

Enter, open the trapdoor...

...and climb down the ladder into one of KHUFU'S QUEEN'S PYRAMIDS.

[Khufu's Queen's Pyramids Walkthrough]