Tomorrow, March 17th, is the day that Ireland and all adopted Irish men and women celebrate the Feast of Saint Patrick. Whether you are joining in the festivities or not, you will still want to mark the date on your calendar so that you remember to pay a visit to Calendar Man in Batman: Arkham City
. Doing so on Xbox One, Xbox 360 or Games for Windows Live will be one of the 12 dates needed for the following achievement:
Calendar Man can be found in the basement of the Solomon Wayne Courthouse. You gain access to the Courthouse near the beginning of the game. All you need to do is to talk to him on each of the 12 dates that are circled on the calendar outside his cell.
Alternatively, you can also gain this achievement offline by changing the date on your console. If you're one of the people who want to actually visit Calendar Man on every date needed, the next date to remember will be April 1st.