Rainforest mountain, a string of west coast beaches, and the easiest island weekend from Bangkok.
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Koh Chang is Thailand's second largest island and mostly vertical: a rainforest spine rising to seven hundred metres, with the road clinging to the coast around it. The beaches line the west side — White Sand, Klong Prao, Kai Bae, Lonely Beach — each with its own character, from family resorts in the north to the backpacker end further south.

The interior is the surprise. Waterfalls with swimming pools at the bottom, trails through proper jungle, and a mangrove coast on the east side that almost nobody visits. It is four hours from Bangkok, which makes it the capital's island weekend — and quiet midweek.
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From Bangkok, buses and minivans run to Trat in four to five hours, and the car ferries from Laem Ngop and Ao Thammachat cross in about forty-five minutes. Combined bus-and-ferry tickets are sold as one journey.
Trat also has a small airport with daily flights from Bangkok, which turns the trip into a morning rather than a day.
From the Gulf coast further south, the practical route is back through Bangkok. Koh Chang sits on the other side of the country from Ban Krut, and there is no coastal shortcut.

White Sand Beach is the busiest and the most convenient. Klong Prao is long, quiet and central. Kai Bae has the best sunsets and the boat trips. Lonely Beach is where the music plays late. The east coast is for people who want none of it.