To leave the tourist attractions behind rent a Russian Minsk and follow the road towards the hills. Be warned, this is for the adventurous only, and truly not for the casually committed. Yet this route offers some of the world's most stunning scenery, stops in hill tribe villages, and a motorcyclist's dream of winding mountain roads. Most of these are unpaved and are alternately dusty and dangerously muddy. At a steady pace this route can be done over two weeks or more but at full throttle can be completed in a week.
Most hotels in Hanoi can set up rentals for a Minsk motorcycle which are well known in the northwest and easy to fix. Anything smaller won't be able to handle the more rugged stretches. The loop starts from Hanoi to Mai Chau, Son La, Tuan Giao, Lai Chau, Tam Duong, Sapa and the highways back to Hanoi. Each town is a hard day's ride from the last and offers accommodation, food and petrol. Make sure to fill up on petrol when it's available and it is a good idea to bring a spare canister along in case of emergencies.
Note that this is a unique trip full of little visited regions but its remoteness also means safety is up to the traveller. To lower the odds of unexpected events, contact a tour provider that can organize a package tour with guide and jeep.