This is one of the coolest achievements/easter eggs I've seen in a while. Batman's foe Calendar Man has a disposition for, you guessed it, calendars. And with that comes an unnatural fascination with the major holidays, which is the basis of the achievement 'Storyteller'.
Before you boot up Batman: Arkham City, change the Xbox or PlayStation 3's internal clock to a holiday, such as 12/25/2011 or 11/24/2011. You have to be offline to do this, though, so keep that in consideration. When you load up the game, head over to the basement of Solomon Wayne Courthouse (you know, the one from the beginning of the game) and talk to Calendar Man. Each holiday has its own creepy Calendar Man mini-monologue. After he finishes his rambling, save and quit the game, change the date to another holiday, and repeat the process.
The holidays you need to visit Calendar Man on to get the achievement are as follows: January 1st, February 14th, March 17th, April 1st, May 13th 2012, June 19th 2011, July 4th, August 16th, September 5th, October 31st, November 24th 2011, December 25th. Another note: The holiday's date may change depending on the year. For best results, Google as needed.
- Xbox 360: 10G
- PlayStation 3: Bronze trophy