Travelers do not stumble upon Sapa, Vietnam. They travel there to see the awesome scenery and get a glimpse of the mountain communities in the area.
Most travelers catch night train in Hanoi and arrive in Sapa in the early morning. There are several departure times for night trains - try to catch the earliest. Watch for "phony porters" who will try to help you with your luggage and then try to extort $2 per bag for helping you. Avoid the whole scene by carrying your own bag to the train and keep your ticket in hand until you arrive at your assigned car. There will be a conductor at the car to take your ticket. Guard your ticket closely - you will need it when you arrive in Sapa.
Upon arrival in Sapa you will be offered a ride "up the mountain" by bus or taxi - unless you've made a reservation. Hang back and watch what kind of deal others are negotiating with drivers. Beware - there are "touts" that act a "middle men". They get a % of the fare - the more you pay the more they get.
The trip to Sapa will take 1.5 to 2 hours. Hotels - you can make a reservation, consult a travel guide (online or book) for recommendations, or wait to see where the bus stops. Check with fellow travelers on the bus, some one may have been there before and has a good hotel in mind.
Or - you can ride to the end of the line. The bus will terminate at a hotel. Grab your gear, find a restaurant and have breakfast. This will give you time to survey the situation. Maybe talk to someone who is wearing a day/fanny pack (most people don't carry all their gear with them when they are looking at the scenery) and find our if they're at a "good" hotel.
Some people bypass Sapa and head for the mountain villages. You might check with a local tour agencies and see if you want to arrange a home stay tour for a night or two. This isn't recommended because Sapa has a lot to offer on its own.
Before agreeing to a tour or guide services be sure to check the weather forecast and road conditions in the area you want to visit. Severe rain storms and landslides across roads are not uncommon around Sapa. If you're traveling on to Dien Bien Phu be sure the roads are up to your standards.
Arrange to go to one of the local villages to see what life is like for the mountain tribes (known locally as "ethnic minorities"). It's much different than that of ethnic Vietnamese. Take a trek through the terraced rice fields and the surrounding mountains. Have a plan to stop for lunch or take it with you.
You will have a lot of chances to meet members of the mountain tribes as they work in the fields or in their villages.
Home stays are very popular and offer more exposure to the mountain way of life. Their style of living is unique and well worth experiencing. Evenings are spent watching traditional ethnic music performances and village life. Celebrating has been known to get out of hand when local liquor is consumed. Early morning life involves preparing breakfast, feeding animals, housekeeping and working in the family garden.
Check the amenities when arranging a home stay. Be sure of the sleeping accommodations. Most home stays offer beds with clean sheets, pillows, mosquito nets and western style toilets.
Some home stays (and other tours) offer opportunities to do some serious trekking from one village to another. Some treks can be fairly remote. People are pleasant but be sure to be respect local customs of the people here and ask permission to take photographs.
Before you leave Sapa consider visiting the local market, the garden around Sapa Lake and the cathedral. If you stay in Sapa for most of your visit these attractions are within walking distance, as is Cat Cat Village in the valley below.
Most travelers return to Lao Cai to catch the return night train to Hanoi. The railroad station is rather austere, but there are nearby attractions. There are several restaurants and Internet cafes close by.
You will arrive early enough back in Hanoi to allow for a full day in Hanoi or depart for a trip to Halong Bay.