The classic Thailand route runs top to bottom: city, then mountains, then islands. Travel it in that order and each stage feels like a reward for the last. Fly out of the south rather than doubling back to Bangkok.
The Grand Palace and Wat Pho first thing in the morning, before the heat and the tour groups. Save an evening for the river.
Onward: Overnight train, 12–13 hr. Second-class sleeper, lower berth if you can get it. A flight does it in 1 hr 15.
Old city temples inside the moat, a cooking class, and an ethical elephant sanctuary — one that does not offer rides.
Onward: Flight, 2 hr. Direct to Krabi. Overland is possible but costs you two days.
Railay by longtail boat, limestone cliffs straight out of the sea, and the four-island trip if the weather holds.
Onward: Ferry, 1 hr 45. To Koh Phi Phi. Koh Lanta is the quieter alternative at about the same distance.
Phi Phi if you want the viewpoint and the nightlife, Lanta if you want long empty beaches and an early night.
Onward: Ferry then flight, 3 hr total. Back to Krabi, then 1 hr 20 to Bangkok for your flight home
On seven nights, cut Chiang Mai. Bangkok and the Andaman coast still make a complete trip; the north deserves more than a rushed two nights.
Add Chiang Rai and the white temple, three hours north of Chiang Mai, or slow down and give Koh Lanta a full week.
Trying to fit both coasts into one trip. The Gulf islands — Samui, Phangan, Tao — and the Andaman islands — Phuket, Krabi, Phi Phi — sit on opposite sides of the country with opposite monsoon seasons. When one coast is at its best the other is being rained on. Pick the coast that matches your dates.
Read the full Thailand travel guide or take the Thailand packing list.