High Speed Challenge is the fifth and final Challenge Act of Green Hill 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.
In this Challenge Act, the player must run through a slightly modified first half of Green Hill Act 1. The player must collect Power Sneakers to run faster through the Challenge Act. Badniks, such as Moto Bug, Buzz Bomber, Buzzer, and Crabmeat, appear in the Challenge Act to make things difficult for the player.
The player begins the Act on an elevated section of the stage, just after the normal beginning. From there, they will see a platform with Power Sneakers, which they should use to quickly get across the bridge and continue through the stage. There are Power Sneakers placed all over the stage, and the player must collect the ones along their chosen path in order to reach the Goal quickly.