It's a good idea to wander down all three tunnels just to familiarize yourself with the layout of the place.
Hint 2
That being said, there's not much to find in tunnel 1 (the one at the left as you enter the main room) at this stage of the game.
Hint 3
At the end of the tunnel, you'll find a mural mostly covered with sand; you can just make out the figure of a blue cat in the middle. Remember that for later, like after you've found the burial chamber --
