You could easily lose months in Thailand's varied topography and attractions—some would say anything less than a week at one of the low-cost, high-value spas is a waste of your time in the land of smiles. But to balance expectation with your ambition, this itinerary transposes the must-see chaos of Bangkok with mountain biking in the hill country, surfing and climbing in Krabi, and just the right amount of utter laziness on the beaches of Phuket. Whether or not you take our advice, consider the special Thai Airways pass when plotting your travels. For only $169 you get three coupons that can be used to fly economy class to any domestic airport the airline serves during a three-month period.

Day 1-3: Arrive in Bangkok and explore this cosmopolitan yet culturally rich city while your internal clock gets in line with Thailand time. Visit one of more than 400 glittering Buddhist temples and the ornate Royal Palace, built in 1767 following the sacking of the former Thai capital, Ayutthaya. Book a day trip through your hotel to Ayutthaya, and marvel at its lost grandeur by touring the fascinating ruins. Pick a tour operator that offers a return trip to Bangkok via a boat ride down the Chao Phraya River (even better if that boat has a Thai buffet). Before you leave Bangkok, catch a round of golf at the Kantarat Course, the old Royal Thai Air Force course. It's not elaborate, but the rough on this course is unusual indeed—it runs smack between the two main runways at Don Muang Airport. Just be careful not to hit a landing jet.

Day 3: Take an hour-long flight to Chiang Mai tonight or get on an overnight bus or train (up to 12 hours) if you're looking to save some dough.

Day 4-8: Chiang Mai province, home to Doi Inthanon National Park, is an adventurer's paradise. Let someone else handle the logistics of exploring this mountainous region by signing up for a four-day guided trek or mountain-biking tour—the outfitter will likely also take you to visit several hill-tribe villages. Or design your own mix of hiking, biking, rafting, and waterfall swimming. Just be sure to leave a day in the province to discover its man-made wonders, too. Visit the famous Wat Phratat Doi Suthep, a mountaintop temple that houses holy Buddhist relics and offers an unobstructed view of the city (that's because you have to climb 290 steps, or take a railcar, to get to it). For a slightly more relaxing day, enroll in a course at the Chiang Mai Thai Cookery School and learn how to craft a perfect curry paste.

Day 9-14: Fly to Phuket, which takes only two hours on a non-stop flight, but upwards of five if you have a layover. Spend the rest of the day discovering the city's unique Sino-Portuguese architecture. If you can, time your visit to coincide with May's Seafood Festival and you're in for a real treat. For aqueous pursuits, May is also a great time to visit Phuket, as clear waters and empty swells beckon divers, snorkelers, and surfers. Book your five-night stay through a dive outfitter that includes three days of diving. That will leave you a few days to surf or just relax on powdery-white beaches. Kata Beach is a good place to rent a surfboard or take a two-hour lesson if you're a newbie.

Day 14: After spending the better part of the day on the beach in Phuket, take a bus or rent a car and drive to Krabi (a three- to four-hour trip).

Day 15-19: Krabi's beaches rival those of Phuket, so you should make a point of visiting first-rate Ao Nang and Hat Rai Le, which both offer excellent diving. But the real draws at Krabi are the stunning limestone cliffs and rock formations, such as the ones at Railay Beach, that are a climber's dream (and will give even the most advanced a challenge). If you're new to the sport, head out to Ko Phi Phi, of the world-famous Phi Phi islands, for a day of easier climbing. Take a day off from beach dwelling or climbing to visit a genuine sea gypsy village on the seldom-visited east coast of Koh Lanta. A rented scooter will get you there just fine; it's only 40 miles from Krabi. The sea gypsies, also known as the Chao Lay, have long resisted the ways of the modern world. While you're there, don't miss Otto's Bar on Nice Beach in southern Koh Lanta. The owner can arrange an informal tour of local fishing villages through the mangrove-thick canals in exchange for a small donation to help the tsunami-recovery fund for the Chao Lay.

Day 20-21: Return to Bangkok in the morning and indulge in a massage at the Shangri-La Hotel's Chi Spa, the perfect way to end your trip—and to prep for that inevitable international flight the next day.