Beanbean Castle Sewers is a location that appears in Mario & Luigi: Superstar Saga.
Being the sewers underneath Beanbean Castle, the area is mainly metallic with many pipes around.
Mario and Luigi were sent to Beanbean Castle Sewers by Lady Lima to fix the plumbing to prove they are the heroes. They must hammer the various of leaks in the pipes to fix them. Unforunately for the duo, Lady Lima turned out to be Cackletta in disguise and fixing the plumbing actually took down the forcefield protecting the Beanstar.