Look Out Below! is the first Challenge Act of Green Hill Act 2 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the classic era and is playable only as Modern Sonic.
This Act takes place within a highly modified version of Green Hill Act 2, with the main difference being the level's layout. It has been changed with numerous barriers and crumbling platforms, which must be traversed by the player in order to complete the Act.
In this Challenge Act, the objective is to reach the Goal Ring at the end of the course, while avoiding falling down from the platforms which break as Sonic runs across them. The player must move quickly in order to not lose lots of time from being sent backward through the level.