Story related, cannot be missed. You need to finish the 'Rebellion Lives' main story mission.
*** Spoiler - click to reveal ***You'll get the mission in The Hidden City after returning from Cenote.
Enter the upper city for the first time, and after passing it a longer platforming section will come across the river. On the other side follow the promt and crawl over the window.
Entering the cell will trigger a cutscene, at the end unlocks the achievement too.