Koh Yao Yai and Koh Yao Noi are the two large islands in the center of Phang Nga Bay. Both are quiet, peaceful places, fringed with sandy beaches and clear water. Most inhabitants still make their living by traditional means such as fishing, rubber tapping, and batik-painting. Considering their size and proximity to Phuket and Krabi, it's surprising how little development these islands have seen. During the 1990s many tourists began to discover the islands and the impact was, unsurprisingly, negative. So to reduce the impact on the land and their culture the villagers residing on Koh Yao organized the "Koh Yao Noi Ecotourism Club" to regulate growth on the islands. They've certainly been successful—they even picked up an award for tourism development sponsored by Conservation International and National Geographic Traveler.
A visit to Koh Yao will allow you to experience the local culture and customs while exploring the beauty of the islands (kayaks and mountain bikes are popular transportation options). The Ecotourism Club provides homestays if you really want the full experience of the islands; otherwise, most resorts provide day tours or information for self-guided exploration.