Koh Lanta

This collection of islands is populated by sea gypsies, riddled with spectacular caves and features great diving among its coral reefs.
Island ChainKoh Lanta actually comprises about fifty islands, many with mangrove forests and coral reef beaches. The largest and most popular island is Koh Lanta Yai; the main village is Ban Sala Dan. Tourists stay in guesthouses and bungalows, although nearby islands have camping facilities.
Fishing VillageThe people of Koh Lanta are mainly Thai Moslems, many of whom have mixed with sea gypsies. Most work on plantations, but some live from fishing. Ban Sangkha-U, a traditional southern fishing village, is a good place to experience the character of the local people. There are very few cars in the village, as on most of the island, and the main circular road is unpaved.
Marine LifeKoh Lanta’s beaches do not match those of Koh Samui or Phuket, but they are relatively peaceful: all on the west coast, the nicest are on the northern and southern ends. This coast supports plenty of coral, and dive sites at Hin Daeng and Hin Muang offer rich marine life, including the occasional whale shark. Visibility is best from November to April.
Cave ComplexTham Khao Mai Kaew, in the center of Koh Lanta, is a vast and disparate cave complex with stalactites, stalagmites, a cavern pool and thousands of bats. Taking a guide is recommended; there is a restaurant and guide service near the start of the path to the caves. Some guesthouses arrange transport to the trail. You can get good views of the island from Deer Neck Cape (Laem Khaw Kwang) in the north.
Reference : http://www.circleofasia.com/Koh-Lanta-Thailand.htm