It is located on the first floor of the greenhouse, but you won't be able to light it up from there

Start your search at the greenhouse

Try looking at the problem in a different light

Head up the stairs to the second floor of the greenhouse and enter the room with a red and purple glow. Look through the colored glass here at the room below. You'll see the starting-point-circle at the base of the blue-colored door. When you're looking the right direction, you'll be able to trace a path along the side of the door and then the frame around the doorway where the blue door used to be, then back to the outline of the door.

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You will first have to pass by this one before being able to see it clearly

It is located inside

The place where this one is found is very colorful

There are many flowers growing in and around this place