Ha Giang (pronounced Ha Ziang if you're from the North of Vietnam) is both a city and a province - Vietnam's most northerly province in fact. The city is pleasant enough, but the real fun starts when you head out into the far north from here. Within 30 minutes drive you're into beautiful countryside and winding mountain roads, and some of the most stunning scenery you'll see anywhere in Vietnam. Our recommendation is to rent a motorbike there - there are plenty of places you can do this in the city - and head up towards Meo Vac, Dong Van and the far north. The scenery is "other worldly" - Karst mountains, rice paddies, and winding tarmac roads which make for some of the best motorcycle country we've ever experienced! Take every opportunity you can to eat with the locals, the food is fantastic, and most of the time will be served with local rice wine, which is also excellent. If you're staying in homestays, which are the best option, you'll get plenty of opportunities to enjoy this.
If you are on a motorbike, don't miss the road between Meo Vac and Dong Van - much of the road is carved into the mountain-side, with endlessly amazing views across mountain peaks, hairpins and sheer drops making it an exhilarating ride. The weekly (Sunday) market in Dong Van is well worth a visit - its a big event for the local Hmong, Tay, Nung and Hoa ethnic minorities, many of whom walk in for hours from the surrounding villages.
When you're ready to head south again, there are three sleeper buses a day back to Hanoi.