Switch Palace
From the Super Mario Wiki
In Super Mario World, there are many colored outline squares called Dotted Line Blocks found throughout the various levels. These squares can become ! Blocks by activating the ! Switch at the Switch Palace, an area usually found by accessing the secret exit of an adjacent level (the only exception being the Yellow Switch Palace). The ! Blocks are used mainly as platforms for Warp Pipes, Secret Exits, and ? Blocks, but also contain helpful power-ups. The best thing about ! Blocks is that the Yellow and Green ones always contain the same power up! (Yellow ! Blocks contain Mushrooms, and Green ! Blocks contain Cape Feathers)
