Cool. You'll love it
If you want to push yourself a little and see another place, then you could add on a Halong Bay trip as an overnight excursion from Hanoi. It's too far for a single day trip - the journey is about 3 hours. The scenery is stunning. I did it as part of a wider tour but there are loads of agents who can sort this for you, even if you want until you're in Hanoi.
I did it after a couple of nights in Hanoi, leaving the next morning for Halong bay. Arrived for lunch then spent the afternoon, and night, on a boat in the bay, with a canoe trip added on. If you google Halong Bay you'll see what I mean about the scenery.