Red Switch Palace
From the Super Mario Wiki
The Red Switch Palace is the third switch palace Mario or Luigi encounters hidden in Super Mario World and its remakes. It is found in Vanilla Dome. This level cannot be replayed after it has been completed.
The palace consists of two rooms, which the player has 200 seconds on the Timer to complete. The first room has eight Koopa Troopas, each separated by a Block with one Koopa in a spinning shell, a P-Switch, and Coins above the Koopas. Mario or Luigi can hit the P-Switch located near them and run to the coins above the Koopas (which have changed to Used Blocks). The spinning Koopa can chase Mario below, but it defeats the Koopas it passes. When all Koopas are hit Mario receives an Extra Life. At the end of the room, Mario can spin-jump on the spinning Koopa for another Extra Life. Mario does not have to hit the P-Switch to progress, since jumping from Used Block to Used Block will work also.
The second room is empty except for the Red ! Switch, which can be activated by jumping on it.
When the Red ! Switch is hit, all red Dotted Line Blocks will become red ! Blocks. These blocks help the player progress through levels by filling in certain gaps, and allowing easy access to a few secret exits.
Levels with Red ! Blocks
Red ! Blocks can be found in these levels:
Coding inside Super Mario World indicated that the Red Switch Palace would actually have been encountered much later (in fact, nearing the end of the game at Valley of Bowser).