Did you go back to the manual : If you find objects or unlock part of the game, some clues have to appear, and especially the words for the locked doors. We work together with Playtiles to provide extra clues in the manual for this kind of situations.
I can't reboot the game from my location (christmas thing, you may know), but I think that you miss the U/V larvae. So you have to pass the trial of Llwyn, it's located in the red aera, close to the tomb where you find the armlet, behind the door with a fox head on its pediment. It's a 3 larvae puzzle, but the answers are engraved in dedicated rooms near the door's area (there is an animation on each room when you enter).