Mai pen rai is a thai saying that loosely translates to "It doesn't matter; life will go on." On December 26, 2004, that philosophy was tested to the extreme when a tsunami pounded Thailand's west coast and the islands in the Andaman Sea. For many Americans, those scenes of destruction wiped Thailand off the travel map. In fact, most of the beaches and reefs that had put Thailand high on their list of places to visit suffered only minimal damage. When I reached Thailand again this year, after working in the country on and off for eight years (and being there during the tsunami itself), I saw mai pen rai in action: Along the coast and in the islands, the Thais were rebuilding their homes and businesses, even selling T-shirts poking fun at their misfortune on the beach in Phuket. Now, with many travelers still tsunami-shy, prices are lower, and many popular sites still deserted. As insensitive as it might sound, now is really a great time to go. Here's how.

BANGKOK
Everyone thinks he knows Bangkok: strippers, traffic, palaces. Farangs (as Thais call foreigners) often ignore the capital or rush about on whirlwind tours. But if you explore on foot and visit the less-touristy areas, you'll find an ancient river city that's thriving with active music, food, and bar scenes -- and now a subway and SkyTrain as well.

DON'T MISS Knock off the glittering Grand Palace, the towering Wat Arun temple, and Wat Po temple, home to a giant reclining Buddha, in the morning before it gets too hot. Then hire a boat and driver and explore the canals of Thonburi ($8 for two hours from the pier near Wat Po), where you'll see traditional waterside life. After lunch, walk through one of the city's cosmopolitan neighborhoods, such as Little India or Middle Eastern Bangkok.

DINING Bangkok has a reputed 50,000 places to eat; here are three can't-miss spots: Chote Chitr, a six-table restaurant near the Grand Palace, prepares classical Thai cuisine, such as gaeng som or orange soup, red curry, and an excellent tom yum, a hot-and-sour seafood broth (from $5; 66-2221-4082). Nguan Lee Lang Suan, an innovative Chinese-Thai diner in the city center, specializes in seafood: try the poo phat pong kari, crabs sautˇed with spicy yellow curry, and whole sea bass deep-fried and topped with crushed garlic (from $10; 66-2257-8366). Baan Klang Naam, a more upscale restaurant on the Chao Phraya River in the Rama III neighborhood, specializes in fresh fish, including red-snapper filets steamed with lime sauce and garlic (from $15; 66-2292-0175).

NIGHTLIFE Patpong, the seedy red-light district, is worth a look, but be warned: It's depressing. Instead, hit a music bar, such as Tawan Daeng in the city's northeast, where locals belt out morlam, an electrified Thai country music, and women in cheerleading outfits dance in perfect sync (66-2717-2108). Or rub shoulders with Thai models and expat entrepreneurs at sleek bars such as the Bed Supperclub (bedsupperclub.com) in the Sukhumvit neighborhood or the nearby Q Bar (qbarbangkok.com).

STAY Smart travelers on a budget skip Khao San Road, the backpacker strip, to relax at the Atlanta (from $10; 66-2252-1650, theatlantahotel.bizland.com) in the Sukhumvit neighborhood, which retains a gloriously faded Graham Greene ambience. Closer to downtown, one of hippest new spots is the 75-room Triple Two Silom (from $100; 66-2627-2222, tripletwosilom.com), a boutique hotel with a popular bar.

TRANSPORT Taxis are your best bet for getting to and from the airport and for visiting the temples in the older part of town. Within the city, you can take the SkyTrain or subway (www.bangkokmetro.co.th).

DIVING
Most Thai beaches have dive operators and access to reefs, but scuba afficionados gravitate to three areas that have the healthiest reefs and most diverse marine life.

Ko Tao, Gulf of Thailand
LOWDOWN Accessible by boat from Ko Samui, Ko Phangan, or Chumphon, Ko Tao has 25 dive sites, including some accessible from the beaches, making it an ideal place to learn. The large cluster of dive shops on the island has driven down prices, so full scuba courses can run less than $50 per day.
DIVING See coral pinnacles, granite boulders, and marine life including whale sharks. STAY In an air-conditioned villa at the plush Anankhira (from $200; anankhira.com) or at the bungalows that line the beaches (from $15; kohtaotravelforum.com). Dive with the PADI award-winning experts at Coral Grand Divers (divekohtao.info), which has beginner to advanced courses.
BEST VISIBILITY July to September

Mu Ko Similan National Park, Andaman Sea
LOWDOWN A string of nine islands, the Similans boast Thailand's healthiest and most diverse reefs (though the tsunami damaged one area). Local divers say that many sites that were previously crowded with divers are now all but deserted. DIVING See giant reef walls, heads of brain coral, and massive sea caves home to giant mantas. STAY Similan Scuba Adventures' four-day live-aboard trips depart from Khao Lak (from $400; similan-scuba.com).
BEST VISIBILITY November to March

The Mergui Archipelago, Andaman Sea
LOWDOWN Recently opened to visitors, these 800 islands off Myanmar attract dive pioneers seeking unexplored reefs.
DIVING Healthy coral reefs with delicate anemones and nudibranches, large fish populations, leopard and white-tip sharks; it's very rare to see any other dive boats.
STAY Faraway Sail and Dive Expeditions leads six- to 10-day live-aboard trips departing from Phuket (from $175 per day; far-away.net">far-away.net).
BEST VISIBILITY November to March

BEACHES AND ISLANDS
In the past, travelers usually explored either the west coast, which faces the Andaman Sea (including Krabi, Phuket, and the Similan Islands), or the east coast, which faces the Gulf of Thailand (including Ko Samui, Ko Phangan, and Ko Tao). But now you can visit both in one trip more easily because Bangkok Airways has daily flights that connect Ko Samui and Phuket (from $50; bangkokair.com). Note: Simple guesthouses or bungalows (think bed, mosquito net, toilet, shower) provide the only lodging at some remote beaches. Be sure to arrive at these places before noon so you can walk from bungalow to bungalow, bargaining along the way.

Andaman Coast
REFRESH Even Phuket still has quiet spots. Near the mangrove forests of Sirinath National Park, the JW Marriott Phuket Resort & Spa (from $245; 66-7633-8000, marriott.com) cures jet lag at its on-site spa and its palm tree-lined 10-mile white-sand beach.

CLIMB A short boat ride from Ao Nang beach, near the town of Krabi, climbers search for cracks and holds on Railay Beach's sharply overhanging limestone spires. Local outfitter King Climbers (railay.com) guides beginners and intermediates up over 600 routes, which also attract world-class climbers. Stay on Railay at the funky Bridge House (from $100; railay.com) or on Ao Nang at the Cliff (from $112; 66-7563-8118, k-bi.com), a cluster of luxe bungalows with a pool built into a Lost World-like rockscape.

MULTISPORT Farther south, Ko Lanta retains a slow, blissful vibe. Kayakers can paddle into its sea caves and swimmers can snorkel in its clear waters. SriLanta (from $65; srilanta.com, 66-2712-8858) and the upscale Pimalai Resort & Spa (from $288; 66-7560-7999, pimalai.com), both on the southern end of the island, use tropical gardens with banana, cashew, and mango trees to make their bungalows seem like hideouts.

EXPLORE The Tarutao National Park, near the Malaysian border, is a string of islands so isolated they once served as an Elba-like penal colony. You'll find pristine reefs; untouched beaches thick with palms, waterfalls, and crab-eating monkeys; and basic lodging, such as Pooh's Bungalows (from $15; poohlipe.com). Tarutao's numerous inlets, honeycombed with limestone sea caves, attract serious kayakers, and PaddleAsia runs four- to eight-day custom trips through the archipelago (from $580 departing from Phuket; 66-7624-0952, paddleasia.com) with lodging in local bungalows.

Gulf of Thailand
RELAX Sand fans skip Ko Samui, which has few remaining secluded spots, and head to the pristine Ao Manao beach, near the fishing village of Prachuap Khiri Khan. Visit the clean but basic Hadthong Hotel (from $15; hadthong.com) near Khao Sam Roi Yot National Park, where guides lead hikes into the vast caverns, which house Buddhist shrines.

PARTY Ravers descend on Hat Rin beach on Ko Phangan for its legendary full-moon parties (fullmoonparty-thailand.com), where top European DJs spin funk, house, and trance. But the vibe between full moons is more laid back. Get to Phangan two days early if you're planning to party at the full moon because guesthouses book up. A good place to detox, whether you dance all night or not, is the Sanctuary, a yoga and wellness spa (from $30; thesanctuarythailand.com).

CHIANG MAI
With access to 8,000-foot peaks, Class IV rivers, and hundreds of miles of trails, the northern city of Chiang Mai rivals the world's multisport adventure capitals.

BIKING Mountain Biking Chiang Mai rents full-suspension rigs for everything from 4x4-assisted downhill blasts on singletrack through thick jungle to three-day trips on rutted trails into the foothills of the Himalayas (from $30 per half day; mountainbikingchiangmai.com). Riders looking for longer trips or road-biking tours along the Thailand-Myanmar border should contact Alex Brodard, who's led expeditions in Southeast Asia for 15 years (from $320 for a four-day trip; activethailand.com).

CLIMBING The Crazy Horse Buttress, located in a valley strewn with rock faces, boulder fields, and rice paddies, attracts every level of rock jock, thanks to its wide variety of routes that are as difficult as 5.13. Chiang Mai Rock Climbing Adventures will show you the ropes (from $45; thailandclimbing.com), often under the gaze of monks who live in nearby caves.

HIKING Avoid the standard elephant treks and instead visit the Thai Elephant Conservation Center, where you can take a course in how to ride and handle tuskers (from $100; changthai.com). For a hike on two feet, contact Wild Planet (from $86; thewildplanet.com), whose certified guides lead two- to five-day jungle treks. The International Sustainable Development Studies Institute, a Chiang Mai organization similar to the National Outdoor Leadership School, runs tough three-week trips into the mountains (from $500; isdsi.org).

KAYAKING Sign up with Siam River Adventures for a five-day running of the Nam Wa River. Its Class IV rapids surge through limestone canyons dotted with banana trees and deep caves (from $415; siamrivers.com).