Thailand has a hot season, a wet season and a tourist calendar that does not match either as neatly as the brochures imply. Bangkok is the hub: humid, crowded, and how most people arrive. The north around Chiang Mai is cooler in the hills. The gulf islands and the Andaman side have monsoon patterns that peak in different months, which is why a beach that is perfect in February can be closed or rough in October. Thai is the language. English is common in tourist work and patchy beyond it.
Domestic flights are how you cover the length of the country quickly. Trains exist and are slower. Between islands you will meet ferries, long-tails and minivans, often sold as a single ticket that is several vehicles taped together. Bangkok is taxis, BTS skytrain, boats on the river, and walking in short bursts because of the heat. Dawn and after dusk are the hours that make sense on foot.
The currency is the baht. Cards work in malls and hotels; cash still runs street food and small island businesses. Tap water is not the drinking water. Temples have dress rules that are enforced at the famous ones. A first trip that works is Bangkok plus one other region, beach or north, not an attempt to collect both coasts and a hill tribe village in nine days.
