Underground Maze of Pipes

The Underground Maze of Pipes is exactly what it sounds like; an maze of Warp Pipes that is underground.

It appeared in Misadventure of Mighty Plumber, when Bowser and Mighty Plumber were trying to get to the Pipe Land Coin Treasury. To do so, Mighty Plumber cracked open a pipe that spewed water all over Bowser.

A large amount of the episode took place in the Maze, as Mario and Luigi were trying to stop Bowser while in it.

Apparently, a certain Warp Pipe in the Maze is linked to Castle Koopa, which is revealed when Bowser exits and ends up in the castle.