Day Trips from Hanoi: Ninh Binh, Ha Long and the Craft Villages
Hanoi is unusually well placed for day trips, and the mistake is attempting the ones that are really overnight trips.
Ninh Binh is the best of them by a distance. Limestone karsts identical in geology to Ha Long's, seen from a small rowing boat on a river, with Mua Cave's staircase for the view over the whole valley. Two hours each way, and a full day is genuinely enough.
Ha Long works as a day trip but gives up the part worth having, which is the hours either side of the day fleet.
Sapa does not work as a day trip in any form. Five to six hours each way means ten to twelve hours in a seat for a few hours in the hills. Anyone selling it as one is selling a bus ride.

Transfer To and From Cat Ba Island by Bus
Bookable directly through AsiaByLocals, with a verified local operator.
From USD 26
3.5 hours
