You will earn this achievement following the mission's , Path to the Hidden City.
*** Spoiler - click to reveal ***Lara will find a mural on the wall of the Temple of Life which shows the path to Paititi (The Hidden City). You will have to go back to the ruins on the north side of the nearby settlement and enter a jaguar mouth carved in the wall there. Lara will then need to complete a sequence of trials and puzzles, eventually running into a group of mysterious people which take her to Paititi, The Hidden City.