I have finished with the maze and have destroyed the red shining ball in Maray. Then went to the tree and filled it with water. Went back to Hunrath via the tree tunnel. Now I think I am supposed to go through a door which has been uncovered in the area with the first small laser (the one we practise on). However the door is still blocked by stuff. Is there something I should have done? How can I unblock that door to access the area up the hill?

A bit late, but have you unlocked all 4 the trees?