Wrong temple XD. From the highest temple drop down from the right ledge and you'll get to the big temple below. From there follow this and then make your way to the top-right most checkpoint in that temple.
I just finished the true ending. 2 keys are required for the secret door which can be found on the left wall in the room just before the normal boss. First key is in the left underground, to the right just after the fungus free fall section. Second key is in the small temple with moving waterfalls, which can be found immediately to the right of the big temple below the highest temple, at the top right after the most top right checkpoint.
Define "normal" and "true" ending. I see only one ending, where after you reach the temple high in the sky you are tasked with finding 3 keys to unlock the sky temple door and beat the normal boss.
