You got the key, after you got the key: on the left wall is a block obscured by vines. Pull it out, climb on top then climb up the cliff and over to the right to get into a cave. Push the big button in there to open the doors below. Go down and enter the doors (golden idol). Go all the way back to the elevator, push the green button and go down. Where the lava flows into the room walk up the steps on the right side. Use the whip to move the statue's arm and open a door on your right. Take care of the scorpions and enter. Fowllow the path to another cavern with a bridge over lava.
After this you meet Sophia and later on you can use the key (to free Sophia!)