Warp Pipe
The Warp Pipe is one of the main modes of transportation in the Mushroom World. Warp Pipes first appeared in the arcade game Mario Bros.. Enemies would emerge from these pipes and attack Mario and Luigi. Warp Pipes have appeared in nearly every Mario game since. These pipes were first used for transportation in Super Mario Bros.. Some even led to underground levels and mini-levels.
During the events of Mario & Luigi: Partners in Time, special blue Warp Pipes required Mario, Luigi, Baby Mario, and Baby Luigi to stand on them in order to activate them.
In New Super Mario Bros., some warp pipes acted as mini-cannons, shooting Mario or Luigi high in the air. Mini Pipes, half the size of a regular Warp Pipe, required the brother to use a Mini Mushroom to enter. Also, if Mario or Luigi use the Mega Mushroom, they can kick the pipe, move it in if it is horizontal, or Ground Pound it to make a raised pipe lower to ground level. If Mega Mario or Luigi destroys a pipe, then they cannot go down the pipe anymore.
The Nintendo Comics System comic, A Mouser In The Houser seemed to imply that the Mousers constructed the Warp Pipe system.