Tomb Raider I-III Remastered Starring Lara Croft

Done in TR1 - Sanctuary of the Scion.

Climb up on to the top of the Sphynx's head and, facing in the same direction as the Sphynx is), head to the front left side of its head, facing left.

Look carefully out into the drop and you'll see a pair of Uzi's floating midair ahead of you.

Do a running jump towards them and you'll land on an invisible floor. You'll have two flying enemies to take care of and can grab jump to the side to safely continue.

If you have all secrets in Egypt thus far, you will also earn the stages single secret and unlock the "All Egypt secrets" achievement at the same time.

A video below to explain better;

This is done on Level 12:- Sanctuary of the Scion on the first Tomb Raider Game.

• Head up the stairs at the start of the level and defeat the 2 enemies that come down if you wish.

• Go into the room at the top, and go around the back of the block in front of you to be able to climb on top of it.

• Climb up again to get onto the sphinx's back.

• Look 45 degrees to the left to see a sloped platform that you can stand on. Climb onto that, then run, jump and grab onto the back of the sphinx head. If you want another achievement here, pull up whilst holding the WALK button (cn_RB by default on tank controls or cn_LB on modern) to do a handstand.
  The TR Pet This Cat achievement in Tomb Raider I-III Remastered Starring Lara Croft worth 14 pointsDo a handstand on the Sphinxes face

• Climb up again in front of you then turn 90 degrees to the left.

• Head straight across the back of the sphinx's head as far as can go without dropping off.

• Head to the corner of this area on your right and look down slightly to see the Uzi's floating in midair.

• Tap backwards and do a running jump towards them to land on an invisible platform.

• Collect them for the achievement.
  The TR Do Uzi This One? achievement in Tomb Raider I-III Remastered Starring Lara Croft worth 22 pointsGet hidden Uzis in Egypt

If you're not getting this through the course of your playthrough and want to get to Level 12 quickly, you can use the level skip cheat 11 times to get there quickly from the start of the game. It can ONLY be done on tank controls. The level skip cheat is:-
Hold the walk button, (cn_RB by default) and push forward once to take a step, then backwards once to take a step. Release the walk button. Press and hold either left or right until Lara completes 3 full rotations. (go a little beyond your starting point to be sure). Do a standing forward jump.