With 3 weeks to play with, you can start in the north of Laos entering at Huai Xai and then have a leisurely journey down the Mekong to Luang Prabang. Fly from Bangkok to Chiang Rai in north Thailand and from there take a bus to Chiang Kong from where you can cross over into Laos. From there, let the Mekong be your guide.
Day 1: Journey to Luang Prabang
Once you have completed immigration formalities in Huay Xai, walk down to the left of the immigration building to where the slow boats to Luang Prabang are moored. These used to be commercial vessels for which you had to haggle hard to get a decent price for passage, and you shared the journey with farmers (and often their livestock). Now there are boats specifically assigned for tourists. The journey to Luang Prabang is 2 days of scenic views, sticky rice, and if you are lucky with your fellow passengers, convivial chitchat. You will stop for the night in Pakbeng. Be on the lookout for scams (and this, sadly, includes the children). Don't let people carry your bags for you when you get off the boat. This once very basic little one-street town situated on a rocky bend of the river is now fairly developed. There are a number of guesthouses and even some midrange hotels and chichi cafes.
Day 2: Arrival in Luang Prabang
Continue your slow trip down the Mekong. Enjoy the dramatic forested limestone mountain scenery, the passing rapids, and the village life along the riverbank. You will arrive in Luang Prabang at about 4pm. Once you have checked into your hotel, have a wander and take in the tranquil beauty of this most beautiful of towns. Enjoy the coffee, the baguettes, the wine, and the sunset.
Day 3: Luang Prabang
Tour the area's temples and sights. Try a bowl of Vietnamese pho for lunch. Have a gander around the central market in the daytime and the night market in the evening.
Day 4: Pak Ou Caves
Visit Pak Ou Caves and see the massed Buddhas. In the afternoon enjoy a herbal sauna and massage -- Luang Prabang has become famous for them. Once suitably relaxed, head to where the long-distance ferries stop and watch the sunset as the sun glows red behind the mountain on the opposite bank of the river.
Day 5: Arrival in Phonsavan
Take the bus to Phonsavan. It will be your base from which to explore the Plain of Jars. It's a grueling 10 hours but the incredible scenery is worth the slog. Phonsavan is not a very interesting town (in fact, it's downright dreary). Get fed and watered and call it an early night.
Day 6: The Plain of Jars
The best way to see the Plain of Jars is by booking a tour with one of the guesthouses in town. Most of them offer a package, costing about $14 per person. You can do it on your own, but it's not recommended -- since the jars are spread out in a number of groupings you might miss something significant.
Day 7: Rte. 13 to Vang Vieng
Take the bus to Vang Vieng. This is an 8-hour drive where once again you are treated to some fantastic scenery along Rte. 13.
Day 8: Vang Vieng
Cross the Nam Song River and spend the morning wandering around the limestone outcrops on the other side. After heading back to town for lunch, enjoy the pointless but fun activity of "tubing" -- drifting down the river on an inflated tractor inner tube.
Day 9: Arrival in Vientiane
Take a bus or minibus to Vientiane (about 3 hr.). After lunch, take in some of the sights such as Wat Pha Kaeo and Wat Si Saket. Have dinner in one of the big Lao riverside restaurants by the Mekong.
Day 10: Vientiane
Spend the morning visiting the National Museum and then take a drive around the city, being sure to pass the impressive but very Gallic Patuxai Monument. In the afternoon, visit Talat Sao Market to shop for special Lao fabric and jewelry, or even DVDs and computer games if that's what you fancy.
Day 11: Flight to Siem Reap
You could easily spend another week in Laos exploring the south of the country, but if you don't want to be hurried in Cambodia (and you really don't want to be hurried in Cambodia), it is time to employ aviation. Your destination is Siem Reap in Cambodia (both Lao Airlines and Vietnam Airlines fly this route). Arriving at lunchtime, once you have dumped your bags in your hotel head to the center of town around Psar Chas. Here you can kick back in any of the many restaurants, cafes, or pubs and get a feel for the place. Take a look around the market stocked with all kinds of handicrafts, clothing, and much more.
Day 12: Angkor Wat
Get up early and see the sunrise over Angkor Wat. It's a photographer's dream and a moment you won't forget. Then head over to Angkor Thom and the Bayon. There is nothing in the world quite like the glorious enigma of the Bayon. Check out the other sites around Angkor Thom and then head back into town for lunch. In the afternoon go to Ta Prohm, an overgrown and atmospheric place that makes the set of Raiders of the Lost Ark look pedestrian. As the sun starts to lower in the sky at about 2pm, head back to Angkor Wat to explore its many splendors. Don't forget to look out for the spectacular bas-relief sculptures and endless apsaras.
Day 13: Journey to Battambang
Today you're heading to the western town of Battambang. You can do this in one of two ways -- either by boat or by road. The boat journey is a bit of an adventure, especially in the dry season when the water is low, but the views of life along the banks of the Sangker River are fascinating. The bus is straightforward. Check in and relax at your hotel and in the evening, get a motodup to take you to the Riverside Balcony Bar, an atmospheric wooden building on the river with a huge veranda. After your riverside aperitif, head over to La Pomme d'Amour for dinner. It's an excellent place for hearty French provincial cooking.
Day 14: Battambang
There is not a lot to do in Battambang, but nevertheless it's a nice place to spend a day wandering down the old colonnaded streets and exploring the central market, which, unlike in Siem Reap, is a practical Cambodian affair with few concessions to tourists.
Day 15: Travel to Phnom Penh
Travel by bus to Phnom Penh, arriving about 4pm. Once you have checked in to your hotel head over to Sisowath Quay on the riverfront. Enjoy a margarita at Cantina, something tasty and French at La Croisette, or something overpriced but with a beautiful view at the FCC. When it comes to dining, Phnom Penh has a dizzying choice of venues serving food from every corner of the globe. Why not start with Khmer food? Malis on Norodom Boulevard serves artfully prepared Cambodian dishes from the kitchen of celebrated Cambodian chef Luu Meng.
Day 16: Phnom Penh
Take in some of Phnom Penh's numerous sites. Start with the Royal Palace and the National Museum. Then move on to Wat Phnom. In the afternoon, check out the Psar Toul Tom Poung, also known as the Russian Market. This vast complex sells just about everything you can think of and some things you never could. In the evening, cross the Tonle Sap to the Prek Leap district where you will find a succession of large traditional Khmer restaurants by the river. Many of them also have bands and singers playing often-melancholic traditional songs.
Day 17: History in Phnom Penh
To understand Cambodia's present, you have to understand the horrors of its recent past. Do not expect to enjoy your morning. First take a moto-taxi or tuk-tuk to the south of the city where you will find the Tuol Sleng or S21 Genocide museum. This is an overwhelming but necessary visit to make. It was here that the Khmer Rouge tortured and then slaughtered thousands of men, women, children, and infants. They photographed their victims meticulously before they killed them and thousands of the fading portraits are on view. The range of expressions is heartbreaking. You can then go to Choeung Ek, the Killing Fields, which was the principal place where these thousands upon thousands of people were systematically killed. In the afternoon, you can relax and be alone with your thoughts on a boat trip down the Mekong, watching life unfold along the riverbanks.
Days 18 & 19: Sihanoukville
Take the bus to the beaches of Sihanoukville, find a peaceful place to your liking, order a cold drink, break out the paperbacks, and relax.
Day 20: Kampot & Kep
Take a trip along the coast to Kep and Kampot. Sample the tasty seafood while in Kep. A well-known local specialty is Kep crab in Kampot pepper. It is a must-try.
Day 21: Back to Phnom Penh
Head back to Phnom Penh by bus and try to work out which restaurant, of the many superb and varied choices on offer, you will go to for your last supper. If you like genuine Spanish tapas and paella, try Pacharan near the Royal Palace. It is in a wonderful old French colonial building, with views of both the river and the Silver Pagoda.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.