The French Quarter in Hanoi, also known as the Old Quarter or "hố Cổ" in Vietnamese, is not a single defined area but rather refers to the influence of French colonial architecture and style spread throughout parts of the city. However, if you're looking for the area with the most concentrated French colonial architecture, it's generally around the Hoàn Kiếm Lake and extends to the west, covering areas such as the Opera House, the Sofitel Legend Metropole Hanoi hotel, and the Government Guest House. This area is rich in historical buildings, tree-lined boulevards, and charming cafes that reflect the French colonial period.