The Rogueport Sewers are are series of sewer lines underneath Rogueport in Paper Mario: The Thousand-Year Door. Pipes can be found here that lead to Petalburg, Boggly Woods, Glitzville, Twilight Town, Keelhaul Key, Poshley Heights, Fahr Outpost and the Pit of 100 Trials. An X-naut teleporter is also here.
A small civilisation lives here. Including some Little Mousers, Bandits, Bob-ombs and Toads. This is also the location for the first Black Chest.
The most famous item in the sewers is the legendary Thousand-Year Door, Which serves as the entrance to the Palace of Shadows.