The Side Paths, or Outskirts, are the Luigi's World levels that you need to beat in order to gain access to the Middle Path's levels (and Luigi's Castle too).
DescriptionEditMaze Cave 2, Koindozer Forest and Rainstorm Lake. In the Demo 6, Thunderstorm Valley was in the place of Maze Cave 2 (known as Maze Cave 1 in said demo), Maze Cave 1 was the first level of the Cave, and Skull Ride was the last level before Iggy's Castle. In the Demo 6.5, Maze Cave 1 was renamed to Maze Cave 2 moved to the first Side Path (as another Maze Cave was created), Skull Ride was moved to be the first level of the Cave and Thunderstorm Valley was moved to the Special Zone. Currently to access the Side Paths, you need to find the secret exit of normal levels, they are: Mirror Fort, Really Big Jump and Finish! Bowser Keep.
Carol's plan was to let the player remove one Middle Path door (see image) by beating a side level. When every side level has been beaten, all the doors would have disappeared and all of the Middle Path's levels would be accessible.