First you go to donnut plains 2. Enter the game and continue till you see the second green tube go into it and break the blocks that store the blue shell. Throw it up to the tallest block and then a vine will grow climb the vine and get the key. Then your at the green switch palace.

In Do*** world, World 2. To the left of the pond you'll see a red level with rocks around
the red circle (it is called Do*** Plains 2). Once you find the key and key hole to that,
you will be granted the green switch place. It will be to the left of the level with rocks
around it.

were is it