Hi! There is no key, you need to find and kill the red monster plant. Its in one of the corners of the location.
I see. I might just be stupid then. Wait, no, I AM stupid, so I could have predicted that.
Edit: I am very stupid, because I cannot get further again.
It's easy enough to find, you only need to check two corners of the location, you've already been to the others ;)
And even so, you can safely leave the location and this will not stop the story game.
