Christmas is on the way and that means 2 more dates are closing in, if you want to get the Storyteller achievement/trophy legitimately in Batman Arkham City you'll need to pay a visit to the creepy Calendar Man. Just head through the backdoor to the courthouse and follow the steps down to the basement. He's waiting there all Lector like for you to visit.

The holidays you need to visit him on are a bit random. Here's the full list:

10/31/2011 - Halloween

11/24/2011 - Thanksgiving

12/25/2011 - Christmas

1/1/2012 - New Years Day

2/14/2012 - Valentines Day

3/17/2012 - St. Patrick's Day

4/1/2012 - April Fools

5/13/2012 - Mothers Day

6/17/2012 - Fathers Day

7/4/2012 - Independence Day

8/16/2012 - Feast Day of St. Roch

9/3/2012 - Labor Day

Off course there are a few spurious methods to get the achievement, but I'll leave that up to you to discover on your own.