The Moon is a place in the Subspace Emissary.
Games used in
If you listen closely, you can hear 'aeiou', 'uuuuuuuuuuuuuuuuuuuuuu' and 'John Madden' at certain times. This is a Moonbase Alpha reference. You can also see the Space Core from Portal 2 floating about at certain times.playable characters enemies bosses