The Aqua Shield Challenge is the third 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.
This Challenge Act takes place in a highly modified version of Chemical Plant Act 1. The player is given many constantly-regenerating Monitors which are scattered all throughout the stage, each one containing an Aqua Shield. As such, the Challenge Act requires the player to take advantage of the shield's Bound Jump in order to properly make it to the Goal Ring. Upon completion, this Challenge Act makes the Aqua Shield skill available for Classic Sonic in the Skill Shop.
The Challenge Act begins with an Aqua Shield within reach. The player must grab it and use it to traverse the obstacles throughout the stage. There are many Aqua Shields left in the player's path in case they take damage and lose their current one, as they must have one at all times in order to successfully complete the Act.