One of my favorite places in Vietnam was Da Lat. It's one of the cities in Vietnam that has a lower temperature than the others cities in Vietnam, around 22C. I stayed here for about one week, spent the days hiking, looking for waterfalls, and viewpoints. In the evenings I went out the the nightmarkets and ate streetfood and drank homemade hot soymilk. You should definitely go here if you are in Vietnam.