Bui Vien Street in District 1 is the axis of the backpacker district — a two-block stretch of hostels, cheap restaurants, bars, and street vendors that becomes one of the loudest places in Asia after 9PM. It is resolutely unsubtle: competing bars blast music at each other, tuk-tuks weave through the pedestrians, and vendors press beers into your hand before you've sat down.
It is not for everyone, but it is genuinely alive in a way that many Southeast Asian tourist streets are not. The surrounding area — the Pham Ngu Lao neighbourhood — has the best concentration of budget guesthouses in the city. Street food on the surrounding blocks (especially De Tham Street) is excellent and cheap. Bui Vien is best arrived at around 8PM when the energy is building but before the volume becomes unbearable.