I was in Hanoi in October 2017 before a cruise on the AmaDara. I stayed at the Hanoi La Siesta hotel right in the heart of the old quarter. They were very friendly. When I asked about buying a SIM card for my phone someone went and picked one up for me and charged it to my room. They greeted me by name every time I came in.
I did lots of different things in my 3 extra days. I did a street food tour by motorbike, and another Vintage Vespa tour. I went to the Vietnamese Women’s Museum. If your tour doesn’t go, I suggest doing a water puppet show. I also have an interest in ethnology, so I arranged a visit to the Vietnam Museum of Ethnology for the day after my nighttime arrival, and found that I was too tired to appreciate it.