Nostalgia is an unlockable achievement for the iPhone and iPod Touch Bloons TD game. All Achievements are provided by an app called OpenFeint. You must have OpenFeint installed in order for any achievements to be available.
This achievement is unlocked when you complete the Classic 2 pack on Hard Difficulty. It awards 30 points upon unlock. It is the gold achievement for the Classic 2 pack, as indicated on the achievement's picture.
- Bronze achievement - awarded for completing the pack on easy or higher.
- Silver achievement - awarded for completing the pack on medium or higher.
As indicated by the achievement names, if you complete the pack on Hard Difficulty, you will unlock this pack's bronze, silver, and gold achievements (if they have not been unlocked before). The same goes for completing the pack on Medium Difficulty; you will unlock the bronze and silver achievements.