Beanbean Castle Sewer
The Beanbean Castle Sewers are sewers found down in the underground of the Beanbean Castle. The sewers run Beanbean Castle Town during Mario & Luigi: Superstar Saga. However, the sewers are full of enemies (specifically Spinies and Super Flies), and had leaking pipes until the Mario brothers came.
When the brothers came, Lady Lima, who was actually Cackletta in disguise, pretended to not believe that the Mario brothers were actually the Mario brothers and that they were fake. She told them that the only way to see if they were lying was to go fix the sewers.
Mario and Luigi went plumbing down in the Beanbean Castle Sewers which helped Cackletta and Fawful steal the Beanstar. While they stole the Beanstar, Lady Lima and the Advisors were locked down in the sewers and Queen Bean was forced to eat a Belly Blech Worm.