In the Alpha version of this game called "A Hat in Time", I found a way to explore the spaceship that you see on the main menu.

First open up the "chat" by pressing "t" (There might be other ways to do this), then backspace all the way to the left, and type "EnableCheats", then "CamMode", then "Walk".
After, you should be able to explore most of it.
If you want to see the hat girl, just type "CamMode" again.

There are many unused rooms, and the doors work! :D

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I'm probably not the first to find this but I wanted to show just in case or something.