Instructions
Talk to Nevada after being trapped on the fourth floor of the pyramid to decipher the ancient riddle. If you can unscramble the text, it says "A Secret Tunnel Hides Between the Two Unbreakable Bones! Dig."
Walk to the right side of the room and stand between the pair of strong bone piles.
Dig a hole in the exact center between the permanent bones to uncover a secret tunnel. Enter the tunnel to exit the pyramid.