I can't tell exactly where you need to go (once again, haven't played in a while), but try the dark blue long area near the dark green maybe? Or... is it also dark green. I dunno, top left, at the very least. I remember after fighting bosses those tend to get unlocked. If that's the freezing water area that damages you in it, try equipping the... Sapphire Necklace, I think it was called, to have the water do way less damage. I think that's where you need to go, anyways. If not, try all your elements on whatever element blocks you haven't gotten through yet, you might've gotten a new one and forgotten to use it.
top left is the blue path where it transport you to a certain area where you need all 3 elements to pass the door am missing the one needed to clear the violet one... the freezing water i already got the necklace and explored mostly the whole area and left no stone unturned... there are 3 areas i cannot access of now since it requires a differnent route to approach.. maybe i should combine the whole map to have a better glimpse of the area... i have the wind,bubble,ice,fire and green whatcha macall it ability