Mario's iconic pipes only exist because Shigeru Miyamoto happened to see "a plastic pipe sticking out of a wall" while wandering the streets of Kyoto

gamesradar.com:

The big green warp pipes populating Mario's world are just an accepted feature at this point, but have you ever wondered where they first came from? According to an old interview with series creator Shigeru Miyamoto, the idea was inspired by a real-life pipe the designer just happened to see while wandering around Kyoto.

This comes from a Japanese interview from 2000, which was initially published in volume one of Game Maestro, and has now been translated by Shmuplations. In it, Miyamoto discusses Mario's origins, including the old enemy ideas Nintendo came up with. Other than the turtle-like Koopas, "we came up with crabs and flies," he revealed. From this, the team "figured the only environment with all three of those creatures – turtles, crabs, and flies – would be an underground tunnel," which Miyamoto suggested "must exist somewhere… like under New York, I thought."

At this point, however, the game's iconic pipes still didn't exist. Instead, they emerged after the team began to consider how to connect the bottom of the screen back to the top, since they needed to have the enemies re-appear there. "So that got us thinking, OK, we need a path or some way for them to get back up there," Miyamoto explained. "Then one day I happened to be walking through the streets of Kyoto, and I saw a plastic pipe sticking out of a wall."

Miyamoto shared a similar story in an 'Iwata Asks' interview with former Nintendo president Satoru Iwata back in 2009, at which point he revealed that the idea to include pipes was also inspired by manga, since "If you read old comic books, there will always be waste ground with pipes lying around." However, he elaborated on the problem the team had faced with trying to avoid the turtles becoming "piled up" at the bottom of the screen, but thinking that "having the top and bottom of the screen connected in the same way [as the left and right sides of the screen] would have been somewhat odd." Thankfully, that's when inspiration struck. 

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