Hanoi Old Quarter is a good choice. There are many colonial buildings that blend Vietnamese and French styles. The scenery is very charming. Walking through it makes people feel like traveling through time and space. Among them, the century-old, sacred and magnificent Hanoi Cathedral "St. Joseph's Cathedral" and the elegant French building "Hanoi Opera House" are famous landmarks.
There are also "36 Ancient Streets of Hanoi" with hundreds of years of history in the Old Quarter. There are many kinds of goods sold on the street. You can have a good stroll. The daytime market will become a night market at night. You can taste many local Vietnamese delicacies and snacks, including Vietnamese French bread (Banh mi), roasted pork rice noodles (Bun Cha), etc. You can arrange to have a big meal there.