Where is the hidden switch for the hidden level in Dedede Resort?

Question

In Dedede's resort one of the stages in the second tier is locked with a question mark on it, and has the following message:

You must press a button found in a specific stage.

In which stage is this button found, and where in the stage is it located?

I would prefer to have the location of the button inside the stage in spoiler text, so I can attempt to find it within the stage on my own.

Answer 1

Take the bottom door at the fork in Dedede Resort Stage 5.

You'll eventually do battle with a giant wooden fish. After you beat it, take the door and swim to the Autocannon and launch your group up to enter a question mark door. Welcome to Stage 6.