In this picture you can see a view from the highest mountain pass in Vietnam, the Tram Ton Pass (Heaven's Gate).
While traveling around this zone, you can experience big weather variations. On one side of the mountain it might be cold and foggy, while on the other side the sun may shine, and the temperature may be warm.
To visit the area you can rent a motorbike in any agency in Sapa. Ask your hotel for more information. Riding a bike in the Northeast region is quite easy. Traffic is almost non existent. You do need to have some experience ridding bikes, though. If you do not feel comfortable riding a bike, book a jeep tour.
If you rent a bike, check it out before departing. Most of the bikes for rent are Chinese replicas of Japanese bikes, and may give you a surprise before the end of your trip.