After exploring the HUGE OCTAGONAL ROOM and side areas, you should have obtained the GOLDEN SERPENT and HAND OF SIRIUS artifacts. If you haven't done that yet, refer to the main walkthrough for details.

Back in the CAVERN, enter the building with the ornate facade on the west cavern wall.

Climb over the block in the middle of the hallway...

...and enter the sandy room beyond.

Notice the sleeping mummy lying on the floor, the 2 artifact receptacles...

...and the opening in one corner of the ceiling high above. That opening leads to the level exit.

If you want all the kills, do not use the artifacts yet. Instead, return past the ornate block...

...to the cavern to find another jackal waiting for you. You may hear it howling if you linger in the passageway.

NOTE: This enemy is also mentioned in the section of the main walkthrough on exploring the cavern the first time. If you triggered this jackal and killed it earlier, it will not appear again.

When you're ready to move on, return to the sandy room with the mummy and place the GOLDEN SERPENT and SCARAB TALISMAN in the receptacles on the wall.

The gate at the entrance closes and sand begins to fill the room, raising the floor gradually. The mummy also awakens and shambles toward Lara. Run around the edge of the room to stay clear of the mummy.

If you keep running, staying fairly close to the walls without running into them, the mummy will try to pursue, but it's not fast enough to catch Lara, so it just ends up groaning and hugging thin air.

After several circuits around the room, the sand level rises enough for you to reach the opening in the ceiling.

Climb out...

...and follow the rocky tunnel toward the light to end the level.

[Burial Chambers Walkthrough]