Rogueport Sewers is a huge chain of rooms under Rogueport that contain the Thousand-Year Door, various Warp Pipes, and the Pit of 100 Trials. There is a hidden town here with a shop that sells rare items such as Ultra Shrooms and Gold Bars. There is also a badge seller named Dazzle, who trades them for Star Pieces. Merluvlee's house is also located here, where Mario can pay her to find the locations of Star Pieces or Shine Sprites, or what to do next. Lastly, there is Wonky's house who Mario can pay to give certain information about the game.
The main way of getting into the sewers is a pipe in front of Professor Frankly's house. Another way in is West Rogueport's sewer grate. Special blue pipes leading to Petalburg, the Great Tree, Keelhaul Key and Poshley Heights can be found in the sewers.
Regular portals to particular regions include a stone warp pipe to Petal Meadows, two wooden pipes: one to Boggly Woods and one to Twilight Town, although the one to Boggly Woods is monochrome like the rest of the woods and the one to Twilight Town is brown with exaggerated shadows, and a blue warp pipe is used to gain access to Fahr Outpost. The teleporter is the fourth portal found in Rogueport Sewers and is used to reach the X-Naut Fortress and through that, the moon after Mario is fired out of the cannon, as it is impossible to be fired again. After completing Chapter 7, this teleporter cannot be used until after completing the game.
When Mario reaches the bottom floor of the sewers for the first time, he has to learn a new paper ability to reach the door from the first Black Chest Demon inside a black chest. After Mario reaches the Thousand-Year Door, he has to stand on the pedestal and hold up the map. The map shows him the location of one of the Crystal Stars. This process is repeated after every Crystal Star Mario gathers.
The entrance in the sewers
Mario and his partners can go west to the 1,000-year-old underground town and to the eastern areas. The entrance contains a Save Block in front of the pipe. Three warp pipes can be accessible to two fortune tellers' houses and the second sublevel of the east. The pipe to Chet Rippo's house in the background is blocked by a cracked wall, which requires Admiral Bobbery's Bomb ability (after Chapter 5). The pipe to sublevel 2 can accessed, either via a floating platform or past the bars via Paper Mode. The pipe to Merlee's house in the background is behind bars, which requires Paper Mode. There is a chest up high, which can be accessed from the sea room, and the player can use Bobbery to make a hole in the wall and reach back to the entrance and obtain the Defend Plus P badge. In the prologue, Mario, Goombella, and Frankly run into three members of the Goomba family tree and defeat them in a tutorial. There is a plane panel that Mario can only use with the Plane Mode ability to glide down to the water room.
The area east of sublevels 2 and 3
To the east of the second sublevel, Mario and his partners reach an area with a large number of enemies. The area features a spike room behind an enclosed cell that can be accessed using Paper Mode. In the room, spikes pop out every three seconds and require Vivian's Veil ability to pass. The Spike Shield badge can be obtained from this cell. In the rightmost area, there is a large yellow block that can be destroyed by using the Super Hammer. Mario can use the first two blue pipes in the area as shortcuts to Petalburg and The Great Tree.
In-game map description
"The ruins of an ancient town remain intact underground, and deep within them is the legendary Thousand-Year Door. Holding the Magical Map aloft before that door will lead to the Crystal Stars."
Additional items are on sale at the Deepdown Depot as well as dropped by enemies.
Hidden ? Block
Names in other languages