Secret treasure locations for those who want them:
Grass: level 10, stand by the torch and wait for the saw to pass then backtrack to beginning of level.
Water: can't remember the level umber now but the level title i think is "block bridge". After pushing the block off of the moving piston, continue walking and jump down the hole without water.
Fire: level 25. After grabbing the key, jump up to the rock jutting out of the wall and then jump again