The Avatar became aware of the Kotl Gem, when Oaxtepac of the Nahuatla Tribe told how it would open the entrance to the lost city. However, he added that it had been stolen by the Urali Tribe on one of their raids.
In a twist of fate, Aiela showed the gem with which Darden had tried to buy her love. It was the Kotl Gem and Oaxtepac advised the Avatar to keep and use it. The Avatar did so. Going to the north end of the Great Mesa, the gem was put into the fitting socket. At noon the sun shone on it, and it opened the secret entrance to Kotl.