While it is possible to visit some of Hanoi's main attractions in a single day, spending only one day in the city might be quite rushed and you will likely not have time to fully experience all that Hanoi has to offer. A more leisurely 2-3 days would allow for a more enjoyable exploration of its rich history, culture, delicious street food, and vibrant atmosphere. However, if you prioritize your sightseeing and plan efficiently, you can still make the most of your one-day visit.