The sewers are, like the name suggests, sewers with water on the floor and ladders that lead to other places. The first area doesn't have much and leads to the Sugar Hole. After leaving the Sugar Hole the second sewers area is the place that will lead to various other areas. It is also the habitat of strange shadow creatures.
The sewers are also the entryway to the Bloody Room Event.
- There is a sewer area in Yume Nikki, making this a possible reference to that area.