I had an idea for a gateway mission that goes into Rosey's fat butt. The spacious anomaly is that people are downsized by going through the portal. Inside Rosey's butt there are various monsters, butt monsters if you will, and they need to be killed. If you go deep enough into Rosey's fat butt, you'll eventually find a treasurehole, filled with advanced technology from ancient civilizations that Rosey may or may not have eaten.
Rosieey's butt is fat.