From the Super Mario Wiki
Chapter 4-4: The Mysterious Mr. L
The Whoa Zone is frequently described as a both a 'Space Graveyard' and a 'complicated maze' by Squirps - upon the heroes' arrival, he tells them to meet up with him later where he will be waiting near the Pure Heart before promptly running off.
The zone is indeed a very complex structure - there are numerous doors in every room, and Mario and co. must utilize special switches and doors that alter the area's gravity, allowing them to walk on the walls and ceilings and reach new sections of the maze. The boss of the Whoa Zone is Mr L and his robotic 'brother', Brobot - following their defeat, Squirps reveals to the heroes that he is the prince of a space kingdom, Squirpia, that once dominated the Whoa Zone, as well as regions of Outer Space around it, and that he was sealed in a hibernation capsule at the request of his mother, so that he could lead Mario and co. to the Pure Heart, which he proceeds to give to them.
Whoa Zone Beta
The Whoa Zone appeared differently in the beta version of Super Paper Mario. It was briefly shown in Super Paper Mario's first trailer, where it was shown to have seemingly more circular elements in its background; the circles shown in this background were orange rather than the green color used in the final game. The Whoa Zone's greenish-brown doors were also normal, red doors in the beta game, and Mario was shown to wear his Space Helmet inside it during the trailer.
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