The following tour is the most comprehensive, and it still hits only the highlights. You can combine any itineraries listed with the side trips and specialty itineraries, and lots of Vietnamese destinations are conducive to further in-depth study or relaxed lingering.
Day 1: Arrive in Hanoi
"Honey, were there five people on that motorcycle?" Yes, dear, there were. Welcome to Hanoi. Even your ride from the airport can be tiring; plan to rest a bit when you first arrive. If you can swing it, stay at the Sofitel Metropole in the heart of the city. Explore the Old Quarter in the evening.
Day 2: Hanoi
Take a Hanoi City Tour starting at the Hanoi Citadel, including the Ho Chi Minh Mausoleum, House, and Museum as well as the One-Pillar Pagoda. Then hit Van Mieu, the Temple of Literature, in the afternoon. Take a tour of the Old Quarter on foot (with or without a guide) or by cyclo. In the evening, take in the Thang Long Water Puppet show. Then collapse.
Day 3: Hanoi to Halong Bay
Leave early in the morning for a 3-hour drive to the pier at Halong City and then board an overnight boat in the bay -- best is the luxury Emeraude, and one notch down is Buffalo Tour's Jewel of the Bay or Handspan Tour's Dragon's Pearl. You will lunch aboard the ship, cruise for a few hours with stops at various cave sites, and then sleep onboard the boat moored in a quiet bay. Itineraries vary, but most include time for kayaking to caves and island lagoons and swimming.
Day 4: Halong Bay to Hanoi
Awaken to sunlight reflecting off the high limestone formations of stunning Halong Bay. Most trips include a morning kayak adventure and a few stops before returning to the pier and making the 3-hour road connection to Hanoi. Overnight in Hanoi. Note: Some adventure itineraries include extra days for more far-ranging kayak exploration, or include an extra night on Cat Ba Island.
Day 5: Hanoi
Enjoy another near full day in Hanoi. Wake up early (dawn) and exercise with locals around Hoan Kiem Lake, check out the lakeside temples, and explore the Old Quarter. Here you can shop, check out the old prison known as the Hanoi Hilton, take in one of Hanoi's museums -- the Vietnam National Museum of Fine Arts is quite good -- see the Opera House, and spend some time near Nha Tho, the Catholic cathedral of Hanoi, with its many shops and cafes along Nha Tho Street. In the evening, catch the overnight train from Hanoi to Lao Cai.
Day 6: Lao Cai to Sapa
Arrive in Lao Cai at 6am and hop on a bus for transfer to Sapa. Check in to your hotel -- I recommend the Victoria Sapa -- and take an afternoon walk down into the valley lined with rice terraces to the Cat Cat Village.
Day 7: Sapa
Spend a full day trekking -- best arranged through an outfitter in Hanoi or with Handspan or Topas in Sapa. The Lao Cai-to-Ta Van Walk is popular, but there are many options to visit Hmong and Dao villages. Explore the Sapa market in the afternoon and take in a dance performance of local hilltribe people in the evening.
Day 8: Sapa to Hanoi
Should you time it right on a Sunday, you can make a round-trip to the Bac Ha Market in the early morning before returning by overnight train to Hanoi. Otherwise, arrange a short day trek, rent a Minsk motorcycle to explore on your own, or take a self-tour through the valley from Sapa before you get on the overnight train from Lao Cai back to Hanoi.
Day 9: Hanoi
When you arrive in Hanoi, you'll likely be tired after trekking and the overnight train. Rest in the capital for the morning and then take a day trip to the handicraft villages outside of Hanoi.
Day 10: Ninh Binh (or the Perfume Pagoda)
Take a day trip out of the big city. Connect with a good tour provider for a full-day trip south of the city to the Ninh Binh area, with the high grottoes of Tam Coc (similar to Halong Bay's, but along a river), and nearby Bich Dong Temple, or visit Ken Ga, a riverside village. You can also include a visit to Cuc Phuong National Park, though it's best as an overnight so that you can go jungle trekking in the morning, when it's cool and the wildlife is active. Another option is to take a full-day tour to the Perfume Pagoda just south of Hanoi. Return to Hanoi for your last evening and some more exploration and shopping.
Day 11: Hanoi to Hue
Fly to Hue in the morning. After checking in at your hotel, take a tour by bicycle or cyclo to the central Hue Citadel and the ruins of the old Imperial City. In the afternoon, you can ride a bicycle -- a little far -- or arrange a car to visit a few sights on the outskirts of town, including a few temples and the Tomb of Tu Duc or other imperial tombs if you have time. In the evening, enjoy dinner at Tropical Garden. After your meal, stroll along the Perfume River near the Trang Tien Bridge.
Day 12: Hue to Hoi An
In the morning, take a boat trip to the Thien Mu Pagoda and visit a few of Hue's many imperial tombs -- best are the tombs of Khai Dinh and Minh Mang. In the afternoon, leave by car or minivan for Danang. Along the way, stop at Lang Co Beach and the overlook at Hai Van Pass. Visit the Cham Museum in Danang and, time permitting, the Marble Mountains. Overnight in Hoi An. If you arrive before the shops close, place an order for your tailored clothes.
Day 13: Hoi An
Take an all-day tour of the central area of Hoi An, stopping at ancient attractions including the Chinese pagodas and congregation halls, the Japanese Bridge, and the many museums and old shop houses. In the afternoon and evening, take in the old town or scoot out to Cua Dai Beach, a short car ride from town, to dip your toes in the South China Sea. Shop 'til you drop in the evening until around 9pm, when shops close.
Day 14: Hoi An
Take a day of leisure and shopping -- get that suit fitted properly -- or beachcombing at Cua Dai Beach, or opt for the all-day jaunt to My Son, the most famous relics of Cham civilization.
Day 15: Hoi An to Nha Trang
Fly from Danang (via a trip to the Marble Mountains in the morning if you've yet to go) and get settled in Nha Trang for a few days of beach time. Rest and relax at the Ana Mandara if you can afford it; if not, good budget options abound, too.
Day 16: Nha Trang
Enjoy the beach, take a scuba course, hop on an all-day boat trip to outlying islands, or hit the city's few nearby sights (the Po Ngar Cham Towers or the Alexandre Yersin Museum). Morning trips to the city market or the fish market near the Po Ngar Cham Towers are popular for photographers. But don't feel pressed -- Nha Trang is a place to kick back, eat good seafood, and rest.
Day 17: Nha Trang to Dalat (or Stay in Nha Trang)
Note: This trip to Dalat is optional; you might prefer to spend an extra night in Nha Trang before flying to Ho Chi Minh City. A 3-hour drive on a spanking new highway takes you to mountainous Dalat. If your budget allows for it, stay at the luxurious Sofitel Dalat Palace or the Ana Mandara Villas Dalat, tucked away on a hilltop overlooking the city center.
Day 18: Dalat
Take a fun day tour of the breathtaking (some rather hokey) sights around Dalat. Hire an Easy Rider and watch out for the bugs hitting your teeth as you smile, bouncing around hilly Dalat on the back of a motorbike (tour options by van and car are also available). Alternatively, try an all-day adventure of trekking, canyoneering, or mountain biking with Phat Tire Ventures.
Day 19: Dalat to Ho Chi Minh City (Saigon)
Starting in the morning, drive overland from Dalat. (Note: Naturalists, birders, and nature photographers will want to add a day at the Cat Tien National Park, about halfway btw. Dalat and Saigon.) Arrive in Ho Chi Minh City in the late afternoon, check in somewhere near central Dong Khoi Street, and then explore the downtown area near Lam Son Square, the central Opera House, and busy Le Loi Street. Lots of good shopping, dining, and nightlife.
Day 20: Ho Chi Minh City Tour
In the morning, get an early start at Giac Lam Pagoda, Ho Chi Minh City's oldest pagoda, and then tour Chinatown and some temples, as well as the large Chinese market, Binh Te Market (all in far-off District 5), before returning to the city center and Ben Thanh Market -- a good place to wander and pick up a few trinkets and stop for lunch at Pho 2000, just adjacent to the market. In the afternoon, hit the War Remnants Museum and, time permitting, the Reunification Palace. In the evening, enjoy a meal at Quan An Ngon Restaurant, Vietnam's finest purveyor of authentic Vietnamese cuisine in an authentic local setting (there are lots of gussied-up high-end Vietnamese restaurants in town, but funky Ngon takes the cake).
Day 21: Cu Chi Tunnels and the Cao Dai Holy See
Leave early to catch a midmorning service of the unique world religion of Cao Daism, in their Technicolor temple. Then make your way to the Cu Chi Tunnels, where North Vietnamese guerrillas waged war on American and South Vietnamese forces from a vast, undetectable complex of tunnels near the terminus of the Ho Chi Minh Trail.
Day 22: Ho Chi Minh City to Chau Doc
Note: Take a guided tour to the Mekong Delta. Most tour providers offer different versions of the same trips, with 1-, 2-, or 3-night stays. Go for at least 2 nights.
Early in the morning, head for the delta -- the rice bowl of Vietnam. Make your first stop the Cai Be Floating Market for a boat ride among the busy river throngs, and then go all the way down to Chau Doc (stay at the Victoria Chau Doc) -- a full day's drive with stops and little side trips.
Day 23: Chau Doc to Can Tho
In the morning, take a boat trip along the canal to the floating villages of ethnic Cham -- you'll see fish farms and riverside temples and mosques near Chau Doc. Then, time permitting, trek up little Sam Mountain, a Buddhist pilgrimage peak with views all the way to Cambodia. Afterward, make your way to Can Tho. Overnight at the Victoria Can Tho.
Day 24: Can Tho to Saigon
Take a morning boat tour along the many canals around Can Tho, visiting craft communities, rice-cake and toffee factories, and raw-rice granaries (photographers will be click-click-clicking) before making your way back to Saigon.
Days 25 to 28: Saigon to Siem Reap (Angkor Wat)
Take a morning flight from Saigon to Siem Reap, the support town for the stunning temples of Angkor Wat. Give yourself a few days to take in all of the sights at Angkor. Some include further travels in Cambodia; you might consider going to Angkor Wat from Saigon via the Cambodian capital of Phnom Penh (you can go by boat from Chau Doc on the Mekong Delta).
Important note: Once you leave Vietnam, you will have to secure a prearranged tourist visa to reenter. You can enter and exit Cambodia at designated points (overland or by air) and receive a visa upon arrival. You can fly from Siem Reap to Bangkok for onward international connection.