Bangkok
There is nowhere quite like Bangkok. The city is overwhelming and irresistible in roughly equal measure — chaotic traffic, dazzling temples, world-class street food, rooftop bars, ancient canals running beside glass towers. The Grand Palace and adjacent Wat Phra Kaew, with its Emerald Buddha, are the mandatory starting point. From there you could spend days wandering Chinatown, taking boat taxis on the Chao Phraya river, eating your way through night markets, or simply getting lost.
Ayutthaya
A two-hour bus or train ride from Bangkok brings you to Ayutthaya, the former capital of the Siamese empire. Founded in 1350 and sacked by the Burmese in 1767, it's now a UNESCO World Heritage Site scattered with the ruins of dozens of temples and Buddhist monuments. Headless Buddha statues sitting amid crumbling chedis, the famous face of a stone Buddha grown into a banyan tree's roots, and the extraordinary scale of what must once have been one of Asia's greatest cities. Best explored by bicycle.
Chiang Mai and the North
Chiang Mai is a base for the north and a destination in its own right — a city of temples, markets, and cooler air that feels a world away from Bangkok. The old city within its moat has a human scale and enough to keep you busy for several days. The surrounding region is excellent trekking country, and the mountains hold hill tribe villages of Karen, Hmong, and Akha people. A warning: elephant riding is widely available in the north, but most of it involves animals that have been mistreated. Seek out sanctuaries that allow you to observe and walk with elephants rather than ride them — Elephant Nature Park near Chiang Mai is the most reputable.
The Southern Islands
Thailand's southern coastline and islands are the reason many people come. The variety is wide: Phuket is fully developed and can be very crowded, but still beautiful; Krabi province has spectacular limestone karst scenery, with Railay Beach accessible only by boat; Koh Samui has good infrastructure and a lively scene; Koh Tao is one of the cheapest places in the world to learn to dive. If you want quiet, the further you go from the main tourist trail — Koh Mak, Koh Phayam — the better your chances.
Diving and Snorkelling
The Andaman Sea has some of Southeast Asia's best diving. The Similan Islands (reachable from Khao Lak, north of Phuket) offer excellent visibility and diverse marine life. The waters around Koh Tao in the Gulf of Thailand are calmer and particularly good for beginners. The diving season follows the weather: Andaman dive sites are best November to April; Gulf of Thailand sites are open most of the year.
Khao Yai and the National Parks
Thailand has set aside 14% of its land as protected area — 79 national parks and dozens of wildlife sanctuaries. Khao Yai, northeast of Bangkok, is the oldest and most visited: 2,000 square kilometres of forest containing elephants, tigers, gibbons, and over 320 bird species. It's easily reached from the capital and makes an excellent overnight trip. Doi Inthanon in the north is the country's highest peak, known for birds, waterfalls, and cool air. Khao Sok in the south has ancient rainforest and the surreal beauty of Cheow Lan Lake, where you can stay on floating bungalows surrounded by limestone cliffs.
Kanchanaburi
Kanchanaburi is where the infamous Death Railway was built during World War II using Allied prisoners of war and Asian labourers under Japanese occupation. The JEATH War Museum and the Commonwealth War Cemetery are sombre and important. The town sits in attractive river scenery and makes an easy day trip or overnight from Bangkok.
The Food
Eating well in Thailand requires almost no effort. Street stalls, markets, and cheap restaurants serve extraordinary food at prices that make careful budgeting unnecessary. The effort should go into eating widely — different regions have different specialties, and a bowl of northern khao soi in Chiang Mai is a completely different experience from Isaan larb or a fresh seafood meal on Koh Samui.