Hanoi, being the capital of Vietnam, is most recommended to be visited in 3-7 days for exploration. Hanoi offers a combination of rich historical relics and modern urban landscapes, allowing for exploration over varying lengths of time.
If time is constrained, here is the 3-day itinerary you should consider:
1st Day: After reaching Hanoi go to Hanoi Cathedral, Qixu Bridge, Huanjian Lake, and Turtle Pagoda. Then, in the evening one can walk beside Huanjian Lake to enjoy the tranquil romantic nature of Hanoi.
2nd Day: Visits include the Confucious Temple-Hanoi Guozijian, Vietnam Art Museum, Lenin Park, and Bamboo-Silk Lake. In the evening, one enjoys local cuisine and nightlife in Vietnam.
3rd Day: Go to the Old Quarter of Hanoi, visiting Thirty Six Streets, Women’s Museum, and Hanoi Lotus Puppet Theatre. A shopping spree can begin in the afternoon, optional free activities, and then head back in the evening for two.