The Crusader attack in 1204 took place around the Blachernae quarter where the sea wall along the harbor (the Golden Horn) met the Blachernae section of the land walls, which joined the Theodosian triple walls on the landward side of the city. The Crusaders were on the landward side, trying to break into Blachernae, while the Venetians attacked the sea wall along the Golden Horn.
As far as terrain goes, the Theodosian walls were unique, but probably didn't play a major role in the fighting. The Golden Gate, used for triumphal entrances, was about two miles away. There was a palace in Blachernae, as well as several Byzantine style churches. The big-name Byzantine landmarks, like the Great Palace, the Hippodrome, and Hagia Sophia were over two miles away to the southwest. The sea wall and the walls around Blachernae were probably impressive, and may have had patterned brick or stonework, like even modern Eastern Orthodox churches have.
The Golden Horn might help sell the game as set at Constantinople, if your game included the attack on the sea wall. Inland a bit less than a half a mile, was the Aqueduct of Valens bringing water to the city.
A skirmish game based on the Byzantines trying to move supplies into town through one of the gates in the Theodosian walls prior to the actual attack might have some possibilities.
Hope that helps a little.
