Star World

Star World is a mystical road far above Dinosaur Land, but which is linked to various locations around the world. It consists of seven stars, which each serve as a warp point.

In Super Mario World, Mario can access the Star World through secret exitways in certain levels. If he succeeds, he can use Star World and its levels as shortcuts around Dinosaur Land and easily make his way to Bowser's Castle.

Levels
In each of these levels there is a Yoshi Egg that hatches into a Baby Yoshi, you need to feed the Baby Yoshi five enemies in order for it to grow into a fully-grown Yoshi (though a power-up will make it grow faster). Once it has grown, it gets special abilities.

The Giant Gate won't allow you to go to the next star level. Instead, you need to put the Key into the keyhole, which takes you to the warp point. Allowing you to decide whether you want to go to the warp point, or complete the next star level.