In epsisode 1, level 7 (the level of the bees), after the green switch hidden behind a wall right after the elevator block going up and down, you fall down, then if you go to the right you will see 2 blue blocks, blocking the way.
Go to highes floor, just below the top. Go right. Jump in the well and hoover slowly down avoiding the nests and the box. Go as down as you can and you should see the switch in the puddle. From the left (I think) you should find the door you mentioned. At this point however, you should (to my opinion) go back up a bit, and right, to the level exit.