Vietnam is all about the contrast between the chaotic, delicious street food in Hanoi and the quiet limestone pillars of Ha Long Bay. You want to aim for the dry season between November and April to avoid the heavy rain and keep your view of the water clear.
A trip like this usually runs about $3200 for flights and local costs. To keep your cash flow steady, you can use the Discover it® Cash Back card to spread that total out over time.
The 15-month intro window is a deadline, not free money. If you have a balance left over after the 15 months, the bank will start charging interest on whatever remains, which can get expensive fast.