After dealing with the first three enemies, go through the open gate near where the third was standing. The gate then closes behind you. The tunnel beyond seems to have collapsed, leaving ramps on two sides.

Another assassin and 2 pesky bats approach from the top of the ramps.

Focus on the assassin first, then switch to pistols and kill the bats. You'll probably need to advance partway up either ramp to wake the second bat.

Follow the lower hall between the ramps. When you reach the downward slope, a pair of sliding block traps activates.

To get through, position Lara on either side of the passageway, about one walking step back from the first sliding block. Press Look and check to make sure Lara is facing straight ahead along the passageway.

Then, as the first block slides away, sprint forward to clear both blocks.

Or, take a standing jump past the first block and stop. Then repeat the same maneuvers to get past the second block. (Not shown.)

Kill the 3 wild dogs lurking inside: one on the left...

...one on the right...

...and one behind the marble basin.

Go around to the back of the basin to find a wide crack where you can get inside. Pick up the small medipack and WOODEN TORCH.

Light the torch on one of the burning torches mounted on the wall by standing close and pressing Action.

Then use it to light each of the 4 unlit torches. This opens the alcove on the west side of the room.

Drop the torch by pressing the Draw Weapon button. Enter the alcove and pick up wideshot shotgun ammo on the left.

Then use the switch on the right to open a gate elsewhere, letting in 3 more wild dogs.

If you stand in the doorway facing the stone basin, the dogs will come to you. Kill them.

Then return past the sliding blocks to the tunnel with the two ramps. (You may meet another bat here if you didn't kill two of them earlier.) Go to the top of the ramps, where you'll find the gate you just opened. Go through.

[Inside the Great Pyramid Walkthrough]