Did you already get rid of all those hyenas? You can check it at the cave where the nubian boy is outside. If you go into the cave and the boy answeres, there are still some of the hyenas left. If all the hyenas are dead, go back to the digsite and check out the place with the broken trails bridge.
Next, go into the pyramid again where you previously arranged that water/bucket thing, but this time take the other entrance on top of the platform.