Air Holes, found below planet Zebes' surface, are artificial pipe-like structures protruding from floors and walls that strongly resemble Warp Pipes from the Super Mario Bros. series. Indeed, in the 1986 manga, Samus mistakes it for one. Like Warp Pipes, they come in a range of colors and a few of them can be entered by Samus. They are only seen in the 2D Metroid games. There are other artificial structures on the ground found only in Norfair that share more or less the same function as Air Holes, though these have a different appearance and can only spawn Polyps.