Valve released Portal 2 a decade ago, but that doesn't mean all of its corners have been explored. One point of discussion is that the game's climax appears to feature a glaring plot hole involving the Moon. One recent fan theory, however, seems to fix the problem quite simply.
In the final boss of Portal 2, test subject Chell faces off against Wheatley, an AI who has gone mad with power after ousting GLaDOS as controller of the Aperture Science facility. The encounter takes place in Wheatley's lair as the facility collapses, and winning involves firing the portal gun at the Moon. However, based on the environments of both Portal games, the facility is deep underground, so how can the Moon be visible from the boss chamber?
As Reddit user u/ReneeHiii points out, though, it's entirely possible that Wheatley's lair is much closer to the surface than the rest of the Aperture Science facility. There's compelling evidence, too. Earlier in the game, Chell and GLaDOS fall down an elevator shaft into the older sections of the complex. Much of the remainder of the game is spent navigating through different areas to climb back to the upper levels where Wheatley is waiting. Also, Chell's final approach to Wheatley's lair takes her on an elevator ride lasting several seconds, so it's entirely likely that the boss fight takes place in one of the highest levels of the facility.
There is evidence that seems to contradict this point as well, though. During the ending of the game, GLaDOS makes peace with Chell before releasing her from the test center. The player ascends on another elevator through numerous levels of the facility before emerging into a cornfield. This ride lasts nearly two minutes and shows off multiple layers of earth and different industrial areas of the complex. There is no way that Chell could have seen the Moon from GLaDOS's chamber without tons of debris filling the room.
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Simply put, it's not the same chamber. After GLaDOS saves Chell from being sucked into space, Chell passes out. The room she wakes up in is not the same room where she blacks out. The first room is heavily damaged from Wheatley's mismanagement and the boss fight while the second chamber is pristine. It also lacks the scaffolding, pipes, and several other architectural features present in Wheatley's lair.
It's possible that GLaDOS repaired the chamber while Chell was unconscious. She is far more effective than Wheatley, and she has plenty of time if she puts Chell into the same sort of suspended animation that she awakens from at the beginning of the game. It's more likely that Chell simply passed out for a few hours, though, and that GLaDOS relocated them both to a separate chamber with the help of Atlas and P-Body from the co-op campaign.
With all the warping and bending that goes on in the Aperture test chambers, it's not surprising that some players might get disoriented. The Moon problem would be a serious hole in the game's storyline, especially for a developer renowned for engaging narratives and storytelling mechanics like Valve, but this theory provides a clean, convincing answer.
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