a marine national park
Favorite thing: Koh Samet belongs to the Khao Laem Ya-Mu Ko Samet Marine National Park. It's a good place to dive or snorkel, and the beaches are white, incredibly white and - cliché - the water very clear, transparent clear. And because it's a national park you're supposed to pay an entrance fee: july 2002 it cost 200 baht per person (and apparently 20 baht for thai people)
Fondest memory: walking along the little trails that criss-cross the island, and finding wonderful beaches to swim and sunbathe.