Twin Bridges world, but many regular levels feature bridge-themed sublevels.
Bridge levels have a sky background, and feature either flying koopas or line guides. It is easy for Mario to fall to his death in the numerous holes among his path, so a cape is immensely helpful in slowing his descent.
Bridge themed levels in SMW
|Level Themes found in Super Mario World|
|Bonus | Bridge | Castle | Cave | Grassland | Forest | Fortress | Ghost House | Mushroom (Theme) | Sky | Underwater|