This is from Arkham superfan channel Batman Arkham Videos. What happened is that there are 12 calendars hidden all around the map. It’s a big map, so it took a while to find them, but they did.

Batman's Arkhamverse has always implemented ... early in a Wayne International Plaza penthouse if players discover hidden Batsuit and gadget displays before Nightwing delivers it to them.

Harvey Dent, Oswald Cobblepot, Waylon Jones and Edward Nygma assist Batman in the Absolute Universe, serving as his private consultants who help keep him in the loop about the hidden threats ...