A three-kilometre island with clear water, one walking street and no cars.
Find a room before you go.
Koh Lipe sits at the bottom of Thailand inside the Tarutao national marine park, closer to Langkawi than to Phuket. It is small — you can walk across it in twenty minutes — and it has three beaches: Sunrise on the east, Sunset on the west, and Pattaya Beach in the south where the boats arrive.

The water is the reason people come. Reefs start a few metres offshore, day boats reach half a dozen uninhabited islands within the hour, and there are no cars anywhere on the island. The trade-off is the journey and the prices: everything arrives by boat, and it shows on the bill.
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The mainland gateway is Pak Bara pier in Satun province, and the crossing takes an hour and a half by speedboat. Getting to Pak Bara is the long part: minivans run from Hat Yai in two hours, and Hat Yai has both an airport and the southern railway.
In high season there are also direct speedboats from Koh Lanta and Phi Phi, which makes a proper island chain possible from Krabi southwards. Those routes disappear from May to October.
From Langkawi in Malaysia, there is an international ferry — passport control happens on the beach, which is as informal as it sounds.

Sunrise Beach is the swimming beach and the quietest of the three. Pattaya Beach is where the boats land and the bars are. Sunset Beach is small, rocky and the most private. Everything is within a fifteen-minute walk anyway.