The best city in Vietnam that most foreign tourist don't consider visiting
There are some awesome cities in Vietnam which don’t have many foreign visitors. I gotta say there are a lot of them like Bac Ninh, Mong Cai, Binh Lieu, Can Tho, Rach Gia, etc. But as a native Vietnamese, I would not recommend you to visit these cities because there is literally no tourism there, at least not for foreigners. People don’t speak English, signs are in Vietnamese only, no nice hotels, no nothing. There will be a lot of difficulties if you want to travel to those cities.
But on the upside, those are very authentic cities, no tourist, no pollution, you can enjoy the very best experience there. There is one easier option, you contact a trusted travel agency and ask them to arrange your own tour with a private tour guide. I strongly recommend AZ Local Trip. Or you can research for travel guides to go on a trip on your own!
However, you should spend around 2 or 3 days in Hanoi - the capital city before looking for these place above. Hanoi is a tourism city but you can't skip this place once in Vietnam. More about the place at https://azlocaltrip.com/hanoi/