Ko Pha Ngan, Thailand
Why it's controversial: Ko Pha Ngan is the poster child of Thai party islands and famous around the world for its riotous Full Moon Parties. These monthly extravaganzas attract tens of thousands of people to the beach at Haad Rin who leave behind mounds of litter in their wake. The impact is not only environmental, but cultural, too, with locals often complaining of a complete lack of respect from their foreign guests.
Instead go to: Ko Tarutao, one of the wildest islands left in Thailand thanks to its status as a national park. It's here that you can envision what the more northerly islands along the Andaman Sea may have looked like before they succumbed to unchecked development.