After the death of Voidius, Illuminati realized he is underestimating Mario and Luigi. So he sent them here. This place seems to be some sort of dark endless neighborhood. To make matters worse there are 3 species to panic about. They are Striders, Watchers, and Swimmers. Once entering this place, you are completely open to all enemies, and you need to hide. The enemy to least panic about is the Swimmers, they usually appear in a water environment. As Stuffwell discovered, you need to travel down a straight path for awhile. This will get you to Level 11.