The alcove you're aiming for is high on the left (south) wall.
If you need a refresher on rope swinging, there are notes at the end of the TOMB OF SEMERKHET walkthrough.
Start by taking a running jump to grab the first rope.
Slide to the bottom.
Rotate a bit to the left.
Then swing and jump to grab the second rope.
Slide to the bottom and rotate left to face the small opening high on the south wall.
Then swing, jump, and grab the edge of the opening. Then pull up...
...crawl backward to the opposite side of the opening...
...and drop down to find SECRET #1 (45/70), the SHOTGUN (or shotgun ammo), flares, and a large medipack.
Safety drop into the hall below.
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