You will start outside, so head straight into the mound. In the first room, a tile (Tile 10) will be lying on the floor; pick this up but don't place it in the slot just yet. Think of the place like a clock. There are 12 rooms and each room requires a tile. Going up will move Gabriel clockwise around the mound. Two of the rooms already have their tiles in place, room 7 and room 12. That leaves 10 tiles that need to be picked up. Each tile will need to go in the corresponding room, based on the number of snakes shown on the tile.

Go up one room, and you will see a tile is in place. Use the gear icon to take a closer look. It will show 7 snakes, meaning this is room 7; the one before it was room 6, and the next room is room 8.

Continue up again, where you will find two more tiles (Tile 2 and 5), then go to the next room. Here will be another tile (Tile 6) and the Snake Rod; pick this up as well, then move to the next room. The next room has Tile 3, the following room has Tile 9.

Move up yet again to enter room 12. The tile here is already in place, so nothing to do here. Go up two more rooms to find Tile 4, then up again for Tile 6, then again for Tile 11, then finally up once more for Tile 1. That's all of them. You should be in room 5 currently, so go ahead and place the corresponding tile into the slot. Go through each room doing this.

You should end on room 4. Go down one room to room 3 and SAVE YOUR GAME. Use the snake rod in this room, but when you do, the mummies will come to life. If they catch you, it is a Game Over. You will need to make your way up through the rooms. The mummies are easy enough to get past. The first two rooms, just go immediately to the door. The following room will have a mummy block the door. Simply go along the right wall of the room to reach the door. In the next room with 3 mummies, use the vines to swing past them into room 7, where the mural will have given way allowing passage. Use the Snake Rod again on the panel in the doorway (not the one with the tile).

Once inside the inner-mound, walk to the right side to find a sacrificial table. Try lifting the lid to find it is too heavy (don't skip this). There are two bars on the wall behind the table. Take both of these to place them in the table. Try lifting it again (gears icon on the bars). Still won't budge. Do as Wolfgang says and use the dagger on the mummy on the other side of the room. Watch the cut scene and the day ends.