Just a few miles out of the town of Sapa. Rent a scooter and be prepared for the breathtaking scenary that surrounds you the instant you depart the small town.
A scooter with a small basket on the front or access to storage under your scooter seat for your camera gear is a must. You will kick yourself later if you don't bring a nice light tripod.
I rented a scooter in the famous french Northern Vietnamese town called Sapa and got this nice deep green rice field shot. There are abundant in Vietnam but really rich in the north I found.