Agree with the comment below: Sapa would be nice , also Hoi An: there are actually many activities you can do like attend a pottery class or ride a bike , taste the best Banh Mi at Banh Mi Queen, spot the beautiful lantern activity. Da Nang is good too, Ba Na Hills, Bach Ma National Park, Marble Mountains. Let’s connect on ig, have been staying in Vietnam for the past 6 months and will be happy to help if anything.