I've traveled to Hanoi a few times for holidays...it's a fantastic city with heaps to do. More than anything I enjoyed wandering around the street of the Old Quarter. I really like visiting Ho's house too. I took one 2 night trip to Halong bay and I was pretty disappointed...we went with a reputable travel agency and we had a nicer junk (boat) than many other groups but it was still a bit yucky, they all seem to have rats living on them, not very romantic! The water was pretty dirty and full of rubbish, yes the limestone formations were attractive but not worth the 2 day trip. If limited on time I would personally skip that part of the country...quite overrated. However we did a day trip to the Perfume Pagoda which was great fun, you go down a river in these tiny little boats...we had a blast. I have not been to Sapa so can't comment on that.