Hanoi, for all the crazy stuff to see in the day, is not a terribly late night party city, even on weekends. Most of the bars in the Old Quarter (in and around Lake Hoan Kiem), where a lot of the backpacker hostels and young people are located, close at or by 1am. I stayed at the Vietnam Backpackers Hostel (THE party place to stay in Hanoi, and cheap and full of amazing travelers of all ranges), which was honestly, the best place to party before 11 pm. Their bottom floor (the “Downtown” location, there are two locations, a mile apart) is essentially a giant bar/restaurant that becomes basically a nightclub until 11pm. Then you go literally across the street to some of the bars/nightclubs, as the area is packed full of places to dance/party/drink. But at 1am, they all close, and everyone goes to Lighthouse, a trashy/sketchy but fun late night place where you can drink and dance, play pool, whatever, until really late. It’s where everyone goes for the late late night. They also have food vendors outside in the back.
But BE CAREFUL and go in a group. Its a short walk from most of the backpacker hostels, though if you’re staying on the west side of Lake Hoan Kiem, it could be up to a 15-20 min walk back. There are lots of people waiting to take advantage of drunk partiers, either offering taxi service then charging INSANE amounts for a less than 1km ride or people waiting to snatch your purse, camera, etc, and run. A motorbike may be ok, if there are enough for everyone, but NEGOTIATE before, 40,000 ($2 USD) should be good, but expect to pay a little more because its late. If you’re close, just walk. BUT KNOW WHERE YOU ARE GOING, walk in a group, don’t draw attention to yourself (which is hard, you’re drunk and loud), and walk fast and watch out for people approaching you. They wont be armed, but they may try to jump and grab what they can. If you do take a taxi, negotiate and MAKE SURE the meter is off after you negotiate a price, you may be in a mafia taxi. Otherwise, enjoy Hanoi at night!