Which Switch is Which? is the second Challenge Act of Chemical Plant Act 1 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the classic era and is playable only as Classic Sonic.
Played as Classic Sonic, this level takes place in the Chemical Plant Act 1. The player's objective is to simply make it through the given terrain to the Goal Ring. However, several barriers block the players progress. In order to gradually get rid of these hinderences, the player has to find the switch corresponding to the given barrier in order to get rid of it so that they move forward. This is done with every barrier encountered until the player makes it to the Goal Ring.