I arrive in Hanoi next Monday for a nine day trip. So far, the plan is 2-3 days in the city, then to Mai Chau, Ninh Binh and, time permitting, Cat Ba. Any recommendations for these areas, how much time to spend in each and what not to miss? Any other places in the north that should not be missed. (I really don't want to fly anywhere, and don't want to spend more than a few hours on a bus or train).