To get the most out of your Thailand vacation, decide what you'd particularly like to do—party in the big city, lie on the beach, go trekking, and so on—and arrange your trip around the region best suited for that activity. Every region has so much to offer, you'll barely scratch the surface in two weeks. However, if you don't know where to start, the following itinerary will allow you see three very different areas of the country without requiring too many marathon travel days.
Almost every trip to Thailand begins in Bangkok, which is a good place to linger for a day or two, because some of the country's most astounding sights can be found in and around the Old City. You'll probably be exhausted by the pace in a few days, so head down to the beach, where you can swim in clear seas and sip cocktails on white sands. After relaxing for a few days, you'll be ready for more adventures, so head to Thailand's second city, Chiang Mai. The surrounding countryside is beautiful, and even a short stay will give you a chance to visit centuries-old architecture and the Elephant Conservation Center.
Temples and royal buildings, such as Bangkok's Grand Palace, require modest dress (no shorts or tank tops).
Take a taxi to the Grand Palace or an Express Boat to nearby Tha Chang Pier. Wat Po is a 10-minute walk south. Hire a longtail boat to get to the canals and back at Tha Chang Pier. Khao San Road is a short taxi ride from the pier.
Bangkok Airways owns the airport at Koh Samui, and flights there are relatively expensive due to taxes, but if you book online directly from Bangkok Airways, you might get reduced airfare. Nok Air and AirAsia also offer cheap flights to nearby Surat Thani or Nakhon Si Thammarat, from which you can take a ferry to the island.
Late November through April is the best time to explore the Andaman Coast. For the Gulf Coast there's good weather from late November until August.
Hotels in the south are frequently packed during high season and Thai holidays, so book in advance.
A great alternative to heading north to Chiang Mai is to use Bangkok as a base to explore the Central Plains. Sukhothai Historical Park isn't as famous as Ayutthaya, but it is even more spectacular, and it and the surrounding region would make an excellent two- to three-day side trip from Bangkok.
Days 1 and 2: Bangkok
Experience the Old Thailand hiding within this modern megalopolis by beginning your first day with a tour of Bangkok's Old City, with visits to the stunning Grand Palace and Wat Po's Reclining Buddha. Later in the day, hire a longtail boat and spend a couple of hours exploring the canals. On the river you'll catch a glimpse of how countless city people lived until not long ago, in wooden stilt houses along the water's edge. For a casual evening, head to the backpacker hangout of Khao San Road for a cheap dinner, fun shopping, and bar-hopping. For something fancy, take a ferry to the Oriental Hotel for riverside cocktails and dinner at Le Normandie.
Start Day 2 with the sights and smells of Chinatown, sampling some of the delicious food along the way. Then head north to silk mogul Jim Thompson's House, a fine example of a traditional teak abode, with antiques displayed inside. If you're up for more shopping, the malls near Siam Square are great browsing territory for local and international fashion, jewelry, and accessories. The malls also have a couple of movie theaters and a bowling alley—Siam Paragon even has an aquarium with sharks. Later, grab a meal at Ban Khun Mae, then if you've any energy left, head over to Lumphini Stadium for a Thai boxing match.
Days 3 to 5: The Beaches
Get an early start and head down to the beach regions. Your choices are too numerous to list here, but Koh Samui, Phuket, and Krabi are all good bets if time is short because of the direct daily flights that connect them with Bangkok. Peaceful Khao Lak is only a two-hour drive from the bustle of Phuket, and Koh Chang is just a couple of hours by ferry from Trat Airport. Closer to Bangkok, Koh Samet and Hua Hin are three hours away by road. But if you have at least three days to spare, you can go almost anywhere that piques your interest—just make sure the time spent traveling doesn't overshadow the time spent relaxing.
Samui, Phuket, and Krabi are also good choices because of the variety of activities each offers. Though Samui has traditionally been backpacker terrain, there are now a number of spa retreats on the island. You can also hike to a waterfall, careen down a treetop zip line, or take a side trip to Angthong National Marine Park. Phuket is the country's main diving center, offering trips to many nearby reefs. There's great sailing around Phuket, too. On Krabi you can enjoy a relaxing afternoon and cheap beachside massage at gorgeous Phra Nang Beach; go rock-climbing on limestone cliffs; kayak from bay to bay; and watch the glorious sunset from nearby Railay Beach.
Day 6: Chiang Mai
Though it shouldn't be a terribly taxing day, getting to Chiang Mai requires some travel time, so you should get an early start. Wherever you are, you'll most likely have to make a connecting flight in Bangkok; if you're pinching pennies, this actually works in your favor, because it's cheaper to book two separate flights on a low-cost airline than to book one ticket from a more expensive airline "directly" from one of the beach airports to Chiang Mai—you'll have to stop in Bangkok anyway. If you play your cards right, you should be in Chiang Mai in time to check into your hotel and grab a late lunch. Afterward, stroll around the Old City, and in the evening go shopping at the famous night market.
Day 7: Chiang Mai
Spend the day exploring the city and visiting the dazzling hilltop wat of Doi Suthep. Ring the dozens of bells surrounding the main building for good luck. On the way back to Chiang Mai, drop in at the seven-spired temple called Wat Chedi Yot or check out the pandas at the zoo. Chiang Mai is famous for its massage and cooking schools, so if you're interested in trying a class in either—or just getting a massage—this is the place to do it.
Day 8: Lampang
An easy side trip from Chiang Mai, Lampang has some beautiful wooden-house architecture and a sedate way of getting around, in pony-drawn carriages.
A short ride out of town is northern Thailand's most revered temple, Wat Phra That Lampang Luang, which contains the country's oldest wooden building. At the Elephant Conservation Center, between Chiang Mai and Lampang, you can take elephant rides, watch the pachyderms bathing in the river, and hear them playing in an orchestra. Proceeds go to promoting elephant welfare.
Day 9: Around Chiang Mai
Your last day in the region can be spent in a variety of ways. Shoppers can takes taxis to the nearby Hang Dong district with furniture and art shops as well as handicrafts villages such as Baan Tawai; or to Lamphun, which has some pre-Thai-era temple architecture from the 7th century. Active types can head to Doi Inthanon National Park, where there are great views across the mountains toward Myanmar, plus bird-watching, hiking to waterfalls, and wildlife that includes Asiatic black bears.
Day 10: Bangkok
Head back to Bangkok. If you're not flying home the moment you step off the plane from Chiang Mai, spend your final day in the city doing some last-minute shopping at the city's numerous markets, such as Pratunam, Pahuraht, and the weekend-only Chatuchak. Or just relax in Lumphini Park.