Climb up the stone wall in the west. Draw your guns and drop down to the area below. There are two scorpions here. Once they're dead, pick up the small medi pack that's in front of the obelisk. To the left are three doorways. Go through the second one.
Vault onto the stone slab and turn to the right. From here, you can pull onto the top of the wall that separates the three rooms. Jump across to each walkway and pick up a small medipack, some uzi ammo, and a box of wideshot shotgun ammo. Make your way back to the first wall you climbed. Drop back down to the middle room.
There's a narrow doorway in a side wall. Go through it and drop down into the hole. Start crawling through the gap at the bottom of the floor. Just as you get into the gap, stop and draw your weapons. Press the 'Look' key and look into the room ahead. There is a scorpion making its way towards you. Kill it before it gets too close. Holster your guns and crawl into the next room.
Shoot the first jar you come across to find a box of normal shotgun ammo. Once you enter the next room, two more scorpions will attack. There's also a third one hiding in a back corner. Kill them and shoot out the jars in this room to collect some uzi ammo, flares, a large medipack, and a box of wideshot shotgun ammo. Exit and return to the area with the obelisk.
To the west is a doorway that is between some columns. Head inside and notice the double doors on the right wall. Continue forward through the grated doorway. As you walk up the slope, Lara will start looking up to the right. Walk to the right and climb up on the pull onto the block in the right corner. Then pull up to the next floor. There are two grated doors that are closed. One holds a canopic jar and the other has a shotgun and small medipack. Jump to the path in the middle. You can also jump to the next path and pick up some Uzi clips and a box of normal shotgun shells. On either side of the middle path are holes you can reach into. Reaching into the holes will trigger the two grated doors to open, allowing you to get the small medipack, shotgun, and canopic jar. A cut scene will show you the next destination when you pick up the canopic jar.
Drop down to the ground level. Jumping into the pool at the back of the room is optional, but doing so allows you to get many items. To begin, there are some flares at the bottom of the pool. On the north wall of the pool is a small opening. Swim through it. You will end up in a long passageway. Follow it until you get to a wall with a blue square on it. That wall is actually a door. Open it and swim through. Watch the ceiling. There will be and opening where you can catch your breath. It's also a secret area where you can pick up some Uzi ammo and normal crossbow ammo. Face the north wall and jump back into the water. Just after you go through the opening (immediately past the air pocket), turn to the left and swim into the small triangle opening. It can be a little tricky to get in and out, so watch your air supply and return to the air pocket if necessary. Going through the small triangle opening will take you into another secret room where you can pick up a box of wideshot shotgun ammo, a large medipack, some Uzi clips, and some poison crossbow ammo. Return to the air pocket (there is nothing else down here but a closed grate) and fill your air supply. That done, follow the path back out the way you entered.
Go back to the area north of the obelisk. On the north wall there are two columns that have statues on them. To the right of the rightmost statue is a block of sand. Climb onto it and drop down to the other side. On the north wall is a doorway that leads to the room that was shown when the canopic jar was picked up. Enter the room.
There is an empty pool directly in front of you when you enter the room. On the floor is a small medipack... and a scorpion. Kill the scorpion and pick up the pack. Go to the left side of the room. There is another empty pool containing only a scorpion. Near the empty pool is a hole in the ground. Drop into the hole and go through the short tunnel. Pull yourself out of the tunnel and quickly draw your guns. There may be a scorpion very close by--you'll hear it walking around. Kill it. In the corner northwest of the opening you just came out of are some flares. You're now in the area to the east of where we entered.
Drop back down into the room. On the left wall, look between the first two pillars. There is a small alcove that you can climb into. Pull yourself into it. This is the last secret area for the level. Here you can collect some flares, and two sets of Uzi ammo. Return back to the main room.
Look above either empty pool. There are some monkey bars you can use to get to the other side of the room. Once over, climb up to the platform at the center of the wall and press the button. This will trigger a door behind you to open and a scorpion to attack. Kill the scorpion. Make your way over to the door that was just opened. Walk into the small alcove and reach into the hole. The large bowl that was in the center of the room lowers down to another floor. Walk to the hole it left and drop down to the next floor.
There is a large medipack on the wall behind you. Pick it up and look around the room. You can enter the water on the west side and swim under the platform to pick up 2 boxes of normal shotgun ammo. Now, look at the wall behind each of the sitting statues and you should find some holes. Place the canopic jar on the shelf on the east side. Remember that door you were supposed to notice in the room with the pool? It just opened. To get out of here, look for a small opening on the east wall. Climb in and follow the passage. There are some flares hidden in a shadowy corner along the way. Return to the area with the obelisk.
Enter the area with the carved pillars. Go through the doors and you will slide into the next level.