The Diamond District is part of New Gotham. There were several buildings including the Gotham News Building, the Royal Hotel, and Gotham Theatre.
Arkham Origins Incident
The Royal Hotel, where Batman first fought Bane. was located in that district. The original Electrocutioner was killed inside that district by the Joker, and Batman recovered the Shock Gloves from his body. Several Anarky Tags and Enigma Datapacks could be found there. After a certain point in the
storyline, multiple snipers started to occupy the rooftops, which possibly made it the most dangerous district in the game. Extreme caution should be used there, as when one sniper detected Batman, he usually informed the others, and Smoke Bombs were less effective against snipers.
It was also the area where the criminal John F. Baker was killed by Enigma shortly after sabotaging the relay tower in Coventry, in order to tie up loose ends, as Alfred revealed to Batman during the Coventry Tower Deathtrap case file.
Cold Cold, Heart Incident
Anarky's Henchmen rioted in the area after their leader was taken into custody. Batman defused the bombs set by them, and incapacitated the rioters. A part of the cryogenic drill was hidden near the Parking Garage of the Royal Hotel. Several more Anarky Tags could be found.
One part Of the Diamond District looks Unique to Founders' Island Skyline.