Welcome to Hanoi! Or is this goodbye for now? Depending on whether you’re coming or going this will probably be your first or your last Hanoi cache (for this trip, at least).
The cache takes about 8 minutes to walk to from the taxi stand outside the international terminal. There is a sidewalk all the way to the cache, so you can easily go grab it before heading to the city, or you can go grab it before checking in for your departing flight.