In Assassin's Creed Unity, the main campaign is primarily set in Paris.
The game follows Arno Dorian during the French Revolution, beginning in 1789 and continuing through the upheaval that transformed French political and social life. Paris supplies the campaign's dense urban environment, landmarks, crowds, missions, and faction conflicts.
Arno joins the French Assassin Brotherhood and investigates a conspiracy connected with the Templars. Major locations include Notre-Dame, the Louvre, the Bastille area, and other recognizable parts of revolutionary Paris.
Versailles appears prominently at the beginning of Arno's story, but it is not the principal setting for the campaign. London is the main setting of Assassin's Creed Syndicate, which takes place in a later historical period.