Phang Nga province could well be Thailand's most scenic, both above the waves and below them. The huge bay formed by the province and its neighbor Krabi is full of fantastic rock stacks sheltering hidden lakes and lagoons. While to the west the ocean is full of some tiny deserted islands surrounded by great dive sites. In between is a lush jungle, much of which is a national park.
The jewel in the crown of Phang Nga dive sites is the Similan Islands, a chain of nine islands, and not a few rocks, around which are arguably some of Thailand's best. However, it's worth noting that most of these sites are closed during the monsoon season, from May to October.